Patients with severe traumatic brain injury (TBI) often demonstrate impairments in performance monitoring--an evaluative control process that can be measured using the error-negativity/error-related negativity (Ne/ERN) and post-error positivity (Pe). The Ne/ERN and Pe are event-related potential (ERP) components generated following errors, with current theories suggesting the Ne/ERN reflects automatic performance monitoring and the Pe reflects error processing and awareness. To elucidate the electrophysiological mechanisms of performance monitoring deficits following severe TBI, behavioral and ERP measurements were obtained, whereas participants with severe TBI and neurologically-healthy comparison participants performed a modified color-naming version of the Stroop task. Behaviorally, both groups demonstrated robust response-time (RT) and error-rate interference. Participants with TBI exhibited generalized RT slowing; no significant between-groups interactions were present for RTs or error rates. ERP results indicate Ne/ERN amplitude was attenuated in participants with TBI, whereas the pattern of Pe amplitude did not clearly differentiate groups. Findings suggest the Ne/ERN as a potential electrophysiological marker of evaluative control/performance monitoring impairment following TBI. Implications for future research and potential clinical application as well as potential limitations in conducting electrophysiological research in neurologically-impaired populations are discussed.