Objectives: Mindfulness-based interventions have been found to improve facets of attentional control. However, comparison with active control groups has been scarce, and few studies have examined mindfulness as a means to ameliorate age-related cognitive deficits. This rigorously designed randomized controlled trial investigated the effects of mindfulness-based attention training (MBAT) on attentional control in older adults relative to an active control group. Methods: Seventy-four community-dwelling older adults were randomized to 4 weeks of MBAT or an active lifestyle education control group. Pre- and post-intervention, participants completed two computerized measures of attentional control with intermittent assessments of self-reported mind-wandering, with metrics of attentional control and mind-wandering being the primary outcome variables for the study. Additionally, participants completed trait and state measures of mindfulness, the positive and negative affect scale, and homework logs to assess intervention-related engagement. Results: Although we found some evidence for greater reductions in mind-wandering in the MBAT than the active control group, the MBAT group did not exhibit greater improvements in attentional performance. Exploratory analyses revealed working memory as a significant moderator of the observed effects, such that those in the MBAT group with higher working memory showed greater improvement in attentional control. Conclusions: We found partial evidence that brief mindfulness training improves mind-wandering, but not attentional control in older adults. Our study provides preliminary support for working memory as an important moderator of short-duration mindfulness training; however, given the exploratory nature of these effects, replication is warranted.