A sizeable body of literature demonstrates positive effects of mindfulness training on brain, behavior, and psychological processes in both novice and expert practitioners as compared to non-meditators. However, only more recently has research begun to examine the specific mechanisms by which mindfulness exerts these effects. In the current study, we used event-related potentials (error-related negativity (ERN), error positivity (Pe)) to test the hypothesis that performance monitoring is one such mechanism. We conducted a randomized controlled trial in healthy older adults (n = 36), relevant because markers of performance monitoring are known to decline with normal aging. Compared to an active control condition, mindfulness participants showed an increase in the ERN, without an increase in the Pe. Participants in both groups reported a reduction in self-report of anxiety and self-judgment of one's own mental functioning, indicating the subjective impression of benefit from each intervention type. The current results are important insofar as they support the purported self-regulatory functions of mindfulness (i.e., learning to respond, not react), as well as demonstrating that such positive effects can be obtained in an older adult sample, both of which have important implications for intervention.