Mind wandering (MW) has been recently investigated in many studies. It has been suggested that, during MW, processing of perceptual stimuli is attenuated in favor of internal thoughts, a phenomenon referred to as perceptual decoupling. Perceptual decoupling has been investigated in ERP studies, which have used relatively simple perceptual stimuli, yet it remains unclear if MW can impact the perceptual processing of complex stimuli with real-world relevance. Here, we investigated the impact of MW on behavioral and neural responses to faces. Thirty-six participants completed a novel sustained attention to response task with faces. They were asked to respond to upright faces (nontargets) and withhold responses to inverted faces (targets) and to report intermittently if they were “On task” or “Off task.” Behavioral analyses revealed greater intraindividual coefficient of variation for nontarget faces preceding Off task versus On task. ERP analyses focused primarily on the N170 component associated with face processing but also included the P1 and P3 components. The results revealed attenuated amplitudes to nontarget faces preceding Off task versus On task for the N170, but not for the P3 or P1. These findings suggest decoupled visual processing of faces during MW, which has implications for social neuroscience research.