During mindfulness-based interventions, participants can be invited to bring aversive stimuli to mind while practicing mindfulness in order to help the stimuli become less aversive. However, the mechanisms underlying this process are not fully understood. In this study we explored these by examining the effects of mindfulness practice and stimulus visualization on stimuli associated with electric shocks. Participants were trained on a discrimination between two visual stimuli using a standard electrodermal conditioning procedure, in which one stimulus (CS+) was paired with shock and the other (CS-) was not. They then visualized either the CS+ or CS-, while practicing mindfulness or performing a control activity. Following a brief extinction phase, the impact of these manipulations was assessed during reacquisition. Both mindfulness and visualization of the CS+ led to slower reacquisition of the CS+/shock association, when measured physiologically, and their effects were additive. Moreover, these effects dissociated from participants’ expectancy of shock.