Polymer gears are used extensively in various applications. However, durability issues have been emerging because of friction at gear tooth contact areas. To extend the lifetime of polymer gears, a low-frictional coating has been considered as a possible strategy. In this study, a finite element simulation method was performed to investigate the contact stress between a pair of coated polymer gears. The simulation included various friction coefficients (COFs) for studying the effects of friction during the operation. Numerical results revealed that the friction causes the contact stress to shift over the roll angle, which is attributed to the direction of the sliding friction based on a free-body diagram. We also investigated the effects of coating and found that a thin coating has little effect on the bulk deformation behavior of the gear. Moreover, the stress distribution in the coating at the pitch point was investigated as the COF increased. Under zero friction, three notable stress regions were observed: 1) the center of the surface, 2) the end of the contact, and 3) the overall contact area. As COF was increased in the micro-slip region of the contact interface, both tensile and compressive stresses in the coating increased. This study provides significant aid to engineers for understanding the stress response of the coating applied to polymer gears to achieve an optimal design.