The effect of rheumatoid arthritis (RA) on peripheral muscle parameters is not completely understood. This study aimed to elucidate the influence of RA on peripheral muscle area and whole body skeletal muscle mass index (SMI) using peripheral quantitative computed tomography and dual-energy X-ray absorptiometry in postmenopausal women. This cross-sectional study included 54 postmenopausal women with RA and 86 healthy controls. Peripheral quantitative computed tomography and dual-energy X-ray absorptiometry were used to measure the muscle cross-sectional area and skeletal muscle mass. Muscle strength was assessed using a handheld dynamometer. Additionally, the effects of RA on muscle area and density as well as the bone / muscle area ratio were analyzed using multivariate models. The muscle area index of the thigh and forearm were correlated between both groups (RA: r = 0.357, p = 0.030; and healthy controls: r = 0.608, p < 0.001) and each index correlated with SMI in RA and healthy controls (p < 0.001). Bone / muscle area ratio correlated between forearms and thighs in health controls only (r = 0.547, p < 0.001). The RA group had a decreased thigh muscle area (p = 0.014); the fat area and fat muscle area ratio at the thigh and forearm were significantly increased (all p < 0.001), as well as thigh bone / muscle area ratio (p = 0.015). The RA group also had significantly lower forearm muscle density (p < 0.001). A sensitivity analysis excluding those on bisphosphonates led to similar results. Independent of RA, the thigh and forearm muscle area correlate with each other and with SMI. Differences in the bone / muscle ratio between RA and healthy controls may indicate regional muscle effects of inflammation and inactivity.