This will be a 12-week, double-blind, randomized, placebo-controlled, parallel group, multicenter study to evaluate the safety, efficacy, and PK of oral administration of PG-760564 in adult patients with active RA receiving treatment with MTX. Two oral doses of PG-760564 will be evaluated: 25 mg BID and 100 mg BID. The study will consist of a screening visit followed by a washout period for all disease modifying antirheumatic drugs (DMARDs) and anti-cytokine therapies except MTX. After the washout period, patients determined to be eligible will be randomized to receive either 25 mg BID or 100 mg BID of oral PG-760564, or placebo for 12 weeks. There will be 6 treatment visits and a follow-up visit 4 weeks after the last treatment visit. The primary efficacy endpoint will be the proportion of patients meeting the ACR 20 response criteria after 12 weeks of treatment.