The purpose of this study is to investigate the safety (adverse events, weight, blood pressure, pulse rate, body temperature, abdominal ultrasonography, standard 12-lead electrocardiography, and laboratory tests) of CNTO 3649 when administered once by subcutaneous injection in healthy adult Japanese men or once a week for 4 weeks in Japanese participants with type 2 diabetes mellitus (disorder in which there is decreased insulin in the body or the body's insulin is not effective, resulting in high blood sugar, increased thirst and urine, and many other side effects).

This is a Phase 1, multi-arm and open-label (all knew the intervention of study) study to explore the safety, pharmacodynamics (the study of how drugs act on the body) and pharmacokinetics (the study of the way a drug enters and leaves the blood and tissues over time) of CNTO 3649. The study has been divided in Part 1 and 2. Part 1 includes healthy adult Japanese men and Part 2 includes Japanese participants with type 2 diabetes mellitus. The healthy adult Japanese men in part 1 will receive a single dose of either 10, 30, 100 or 300 microgram/milliliter (mcg/mL) of CNTO 3649 and participants in part 2 will receive subcutaneous doses of either 30 or 100 mcg/mL of CNTO 3649 once a week for 4 weeks. The study will have a Screening period of 28 days for Part 1 and 42 days for Part 2. Participants will primarily be assessed for safety (adverse events, weight, blood pressure, pulse rate, body temperature, abdominal ultrasonography, standard 12-lead electrocardiography, and laboratory test). The total duration of study will be 57 days for Part 1 and 92 days for Part 2.

Inclusion Criteria:

Part 1

• Weighs greater than or equal to (>=) 50 kilogram (kg) and less than (<) 100 kg and has a body mass index (BMI) of >= 18.5 and <25.0 at the time of screening tests
• Is a non-smoker, or is able to refrain from smoking from 2 days before screening tests until completion of post-treatment examinations or follow-up investigations
• Is able to refrain from consuming alcohol from 2 days before screening tests until completion of screening tests, from 2 days before hospitalization (Day -4) until after discharge (Day 8), from 2 days before clinic visits (Days 13 and 20) until completion of tests at clinic visits (Days 15 and 22), and from 2 days before post-treatment examinations or follow-up investigations until completion of post-treatment examinations or follow-up investigations
• Has agreed to use a medically acceptable form of contraception (example [eg], condoms) from the day of hospitalization (Day -2) until completion of post-treatment examinations or follow-up investigations
• Has no clinically problematic abnormalities in medical examinations and tests before study treatment

Part 2

• Weighs >= 50 kg and <100 kg and has a BMI of >=18.5 and <37.0 at the time of screening tests
• Was diagnosed with type 2 diabetes mellitus at least 3 months before screening tests and this is being stably managed with dietary modification, exercise therapy, or sulfonylureas or biguanides If sulfonylureas or biguanides are being used, these have been used at a fixed dosage to stably manage the disease since at least 3 months before screening tests
• If the participant has hyperlipidemia, this has been stably managed with antihyperlipidemic drugs at a fixed dosage since at least 3 months before screening tests
• If the participant has hypertension, this has been stably managed with antihypertensive drugs at a fixed dosage since at least 3 months before screening tests
• Is a non-smoker, or is able to refrain from smoking during the hospitalization period and from 1 day before clinic visit days until completion of tests

Exclusion Criteria:

Part 1

• Has or has had hepatic, renal, central nervous system (including psychiatric), cardiovascular, respiratory, gastrointestinal, hematopoietic, ophthalmic, infectious, or endocrine disease that would make the participant unsuitable as a study participant
• Has had a malignant tumor within 5 years before study treatment
• Has undergone surgery that would make the participant unsuitable as a study participant within 12 weeks before screening tests
• Has or had acute disease that occurred within 7 days before study treatment
• Has or has had an eating disorder (pathological anorexia or bulimia)

Part 2

• If only dietary modification and exercise therapy are being used, fasting blood glucose is <130 milligram per deciliters (mg/dL) or >= 270 mg/dL in screening tests and at hospitalization (Day -1). If oral antihyperglycemic drugs are being used, fasting blood glucose is <100 mg/dL or >= 240 mg/dL at the time of screening tests and <120 mg/dL or >= 270 mg/dL at hospitalization (Day -1)
• If only dietary modification and exercise therapy are being used, HbA 1C at the time of Screening tests is <6% or >= 10 percent (%). If oral antihyperglycemic drugs are being used, HbA 1C at the time of screening tests is <6% or >=9%
• Has blood pressure or a pulse rate that is outside of the following ranges, or has hypertension and blood pressure or a pulse rate that is outside of the following ranges despite taking an antihypertensive drug at the same dosage since at least 3 months before screening tests
• Has or has had type 1 diabetes mellitus
• Has or has had autoimmune diabetes mellitus