The interactive effect of exercise intensity and task difficulty on human cognitive processing was investigated using the P3 component of an event-related brain potential (ERP). Exercise intensity was established using Borg's rating of perceived exertion (RPE) scale, and task difficulty was manipulated using a modified flanker task comprised of incongruent and neutral trials. Twelve participants (22 to 30 y) performed the flanker task during a baseline session, and again after light (RPE: 11), moderate (RPE: 13), and hard (RPE: 15) cycling exercise. Results indicated that the P3 amplitude increases across task conditions following light and moderate cycling, but not during hard cycling, relative to baseline, suggesting that P3 amplitude may change in an inverted U fashion by as a result of acute exercise intensity. Additionally, the expected delay in P3 latency for incongruent relative to neutral trials was observed during the baseline condition. However, following acute exercise these task condition differences diminished across exercise intensities. Moreover, reaction times following all exercise conditions were shorter when compared to the baseline condition. These findings suggest that P3 latency is more sensitive to task difficulty manipulated by a flanker task than behavioral measures, and P3 latency during trials requiring greater executive control processes might be more sensitive to the effects of acute exercise than tasks requiring minimal effort.