Transcranial direct current stimulation (tDCS) exerts pro-cognitive effects in various populations. We evaluated the effect of tDCS on cognitive performance and its electrophysiological correlates in schizophrenia patients. Ten participants received 10 sessions of tDCS and performed cognitive performance tasks; error-related negativity and correct response negativity (CRN) were measured before and after tDCS. Verbal performance was improved by tDCS and strongly correlated with a reduced CRN amplitude. Despite the lack of sham control design and possible practice effects of cognitive tasks, we might conclude that CRN could be a modifiable electrophysiological correlate of cognitive improvement by tDCS.