Numerous studies have shown that the N1 event-related potential (ERP) response is attenuated when it is elicited by self-initiated sounds. This N1 suppression effect is generally interpreted to reflect an internal prediction mechanism, which enables the discrimination of the sensory consequences of our own actions and those of others. The blocked design used in the forerunner studies (i.e., self- and externally initiated sounds presented in different blocks) seriously limits the relevance of these findings, because the N1 effect can simply be explained by contextual task differences. In the present study, self- and externally initiated sounds were mixed within blocks. N1 suppression was found, and its magnitude was even larger than that observed in a traditional blocked condition. This result supports the involvement of an internal prediction mechanism in the discrimination of the sensory consequences of one's own actions and those of others.