Studies report error-processing abnormalities in high-functioning individuals with Autism Spectrum Disorders (ASD) that may be influenced by intelligence and autism severity. Error processing can be measured using the error-related negativity (ERN) and post-error positivity (Pe) components of the event-related potential (ERP), along with behavioral indices such as post-error reaction time (RT) slowing. We used a modified Flanker task to test the hypothesis that high-functioning individuals with ASD would show decreased amplitude ERN in 24 individuals with ASD and 21 age- and IQ-matched typically-developing control participants. Behaviorally, individuals with ASD committed more errors than controls, but groups did not significantly differ on RTs, although there was a trend-level difference in post-error slowing. For ERPs, ERN amplitude was significantly attenuated in individuals with ASD relative to controls; groups did not differ in Pe amplitude. Amplitude of the ERN was not significantly correlated with measures of intelligence, anxiety, behavioral inhibition, or general autism severity.