High impulsive individuals have problems with self-monitoring and learning from their mistakes. The aim of this study was to investigate whether error processing is impaired in high trait impulsivity, and how it is modulated by the task difficulty. Adults were classified as high (n = 10) and low (n = 10) impulsive participants based on the Barratt Impulsiveness Scale, and they participated in a modified flanker task. The flanker trials had three levels of task difficulty manipulated by visual degradation of the stimuli. We measured RTs and ERP components (Ne, Pe) related to erroneous responses. Low impulsive participants responded significantly faster than high impulsive participants. The two groups did not differ in accuracy. The Ne amplitude was smaller in high than in low impulsivity in case of medium and high difficulty levels, but not at low difficulty level. However, the groups did not differ either in the amplitude or in the latency of Pe. We suggest that trait impulsivity is characterized by impaired error detection.