The purpose of this study is to evaluate the safety, tolerability, and pharmacokinetics (PK, study of the way a drug enters and leaves the blood and tissues over time) of single-ascending oral doses of JNJ-54861911 in healthy Japanese male participants.

This is a single-center, randomized (study medication assigned to participants by chance), double-blind (neither Investigator nor participant knows which treatment the participant receives), placebo controlled (placebo is an inactive substance that is compared with a drug to test whether the drug has a real effect in a clinical trial), study of a single-ascending dose of JNJ-54861911 in participants between 55 to 75 years of age. The duration of study will be approximately 2 to 6 weeks per participant. The study consists of 3 periods: Screening period (28 to 2 days prior to dose administration); Double-blind Treatment period (participants will receive either a single oral dose of JNJ-54861911 or placebo as tablets under fasted conditions); and a Follow-up visit period (7 to 14 days after dose administration). All the eligible participants will be assigned to any of following 3 cohorts: Cohort A (single oral dose of JNJ-54861911, 25 milligram [mg] or placebo); Cohort B (single oral dose of JNJ-54861911, 50 mg or placebo); Cohort C (single oral dose of JNJ-54861911, 100 mg or placebo). Each cohort will include 8 participants. Participants in each cohort will be randomly assigned to receive either a single oral dose of JNJ-54861911 (n = 6) or placebo (n = 2). Blood samples will be collected pre-dose and over 96 hours (that is up to Day 5) after dosing for understanding the PK characteristics of JNJ-54861911. Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Signed an informed consent document indicating they understand the purpose of and procedures required for the study, and are willing to participate in the study
• A man, who is sexually active with a woman of child-bearing potential and has not had a vasectomy, must agree to use an adequate contraception method as deemed appropriate by the investigator, and must not donate sperm during the study and for 90 days after receiving the study drug
• Body mass index between 18 and 30 kilogram (kg) per square meter
• Blood pressure (supine for 5 minutes) between 90 and 150 millimeter of mercury (mm Hg) systolic, and no higher than 90 mm Hg diastolic
• Must be healthy on the basis of physical and neurological examination, medical history, vital signs, and 12-lead electrocardiogram (ECG) performed at screening or admission (up to Day 1 predose)

Exclusion Criteria:

• History of or current liver or renal impairment, significant cardiac, vascular, pulmonary, gastrointestinal, endocrine, neurologic, hematologic, rheumatologic, psychiatric, dermatological (at the puncture site) or metabolic disturbances
• History of spontaneous, prolonged and severe bleeding of unclear origin
• History of epilepsy or fits
• History of human immunodeficiency virus (HIV) antigen/antibody positive, or tests positive for HIV at screening