The belief that one can exert intentional control over behavior is deeply rooted in virtually all human beings. It has been shown that weakening such belief – e.g. by exposure to ‘antifree will’ messages – can lead people to display antisocial tendencies. We propose that this cursory and irresponsible behavior may be facilitated by a breakdown of neurocognitive mechanisms underlying behavioral adjustments. In the study reported here, we tested the hypothesis that weakening belief in intentional control reduces cognitive markers of behavioral control. Participants performed a Simon task before and after reading a scientific text either denying free will (no-free will group) or not mentioning free will (control group). Results showed that the post-error slowing, a cognitive marker of performance adjustment, was reduced in the no-free will group. This reduction was proportional to a decrease of the belief in intentional control. These observations indicate that weakening the belief in free will can impact behavioral adjustment after an error, and could be the cause of antisocial and irresponsible behavior.