Abstract Objectives This study aimed to investigate the mechanism of cognitive control impairment in patients with schizophrenia (SPs) using electroencephalogram (EEG). Methods A total of 17 SPs and 17 healthy controls (HCs) were included in this study. We measured the EEG activity, whereas they performed the AX‐continuous performance test which consisted of the preparatory phase and the response phase. The MATRICS Consensus Cognitive Battery (MCCB) was used for cognitive function, and the Positive and Negative Syndrome Scale (PANSS) was used for clinical symptom assessment. A univariate linear regression model was used to explore the relationships among behavioral index, event‐related potentials (ERPs), rhythmic oscillation power, and score of MCCB and PANSS. Results A significant difference was found in response accuracy and reaction time (RT) during the preparatory phase between patients and HCs (p