The possibility that improved inhibitory control in older adults is associated with engagement in non-contact sporting activity, Tai Chi, was investigated. Three groups of participants were compared; a group who regularly took part in Tai Chi (TC), a regularly exercising (RE) group, and a sedentary group (SG). Concurrent electroencephalographic recordings were obtained while a stop-signal inhibitory control task, where speeded responses are needed for most trials, but these must occasionally be withheld when a ‘stop signal’ is displayed, was performed. The electrophysiological components P3, broadly related to decision making, and Pe, related to error monitoring, were analyzed. Both exercise groups performed better on the stop-signal task for the measure indicative of inhibitory control, as well as being generally better for other indices of performance. No significant effects were seen for post-error slowing. Electrophysiological differences were seen for the TC group, with a significantly larger P3 component related to the stop-signal and a larger Pe component when errors were made. This indicated that the TC group seemed to show better decision making and have better awareness of errors. Future work should investigate whether such effects are seen when this type of exercise is applied as an ‘intervention’ in non-exercising individuals.