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Description: Background: Neurophysiological tools have yielded valuable insights into the pathophysiology and treatment of psychosis. However, studies using event-related potentials (ERPs) primarily focus on average/mean scores and neglect within-person variability of ERP scores. The neglect of within-person variability of ERPs in the search for biomarkers might result in missed crucial differences related to psychosis. This registered report aimed to determine whether distinct patterns of intraindividual variability in ERP biomarkers are observed in people with psychosis. Methods: Publicly available data posted to the NIMH Data Archive for 1R01MH110434-01 was obtained for 162 patients with psychosis and 178 people without psychosis. Participants completed tasks that measured auditory mismatch negativity (MMN), P300, error-related negativity (ERN), and reward positivity (RewP). Multilevel location-scale models were used to determine whether people with psychosis show greater intraindividual variability of ERP scores than people without psychosis. Results: Contrary to predictions, groups did not differ in within-person variability of MMN-frequency, P3, or ERN; patients showed less variability in MMN-duration than controls. Exploratory analyses of a subset of patients with schizophrenia showed greater variability in this group than in controls for MMNs. Greater severity of thought disorder and activation symptoms were significantly associated with higher intraindividual MMN variability. Discussion: Distinct patterns of intraindividual variability in the measured ERPs were not observed for the broad group of people with psychotic disorders. Exploratory analyses suggest that intraindividual differences in ERPs are more relevant to certain symptom dimensions than to psychotic disorders broadly, but research is needed to confirm these exploratory findings.