This study is designed to evaluate the safety and efficacy of a dose and dosage regimen of SBI-087 in seropositive patients with active Rheumatoid Arthritis, who are on a stable dose of methotrexate.

Inclusion Criteria:

• Meets the American College of Rheumatology (ACR) 1987 revised criteria for classification of Rheumatoid Arthritis (RA) for at least 6 months prior to screening
• Active RA as defined by >= 5 swollen and >= 5 tender joints (28-joint count) and at least 1 of the following: C-reactive protein >= 10 mg/L or Erythrocyte Sedimentation Rate >= 28 mm/h
• Must be seropositive as defined by a documented history of rheumatoid factor (RF) or anti-cyclic citrullinated peptide (anti-CCP) positivity
• Must be receiving a stable route and dose of methotrexate (up to 25 mg weekly)

Exclusion Criteria:

• Any significant health problem other than rheumatoid arthritis
• Any clinically significant laboratory abnormalities
• Any prior use of B cell-depleting therapy