Mind wandering reduces both the sensory and cognitive processing of affectively neutral stimuli, but whether it also modulates the processing of affectively salient stimuli remains unclear. In particular, we examined whether mind wandering attenuates one's sensitivity to observing mild pain in others. In the first experiment, we recorded event-related potentials (ERPs) as participants viewed images of hands in either painful or neutral situations, while being prompted at random intervals to report whether their thoughts were on task or mind wandering. We found that the brain's later response to painful images was significantly reduced immediately preceding "mind-wandering" versus "on-task" reports, as measured via amplitude decreases in a frontal-central positivity beginning approximately 300 ms poststimulus. In a second, control experiment using behavioral measures, we wanted to confirm whether the subjective sense of pain observed in others does in fact decrease during mind wandering. Accordingly, we asked participants to rate how painful the hand images looked on a 5-point Likert scale, again while taking reports of their mind-wandering states at unpredictable intervals. Consistent with our ERP data, we found that the ratings for painful images were significantly reduced immediately preceding mind-wandering reports. Additional control analyses suggested that the effect could not simply be ascribed to general habituation in the affective response to painful images over time. Collectively, our findings demonstrate that mind wandering can directly modulate the cortical processing of affectively salient stimulus inputs, serving in this case to reduce sensitivity to the physical discomfort of others.