This study recorded brain event-related potentials (ERPs) during an attention task under two conditions: (a) immediately after strenuous exercise and (b) immediately after an extended rest period. The goal was to examine the effect of different physiological states on the electrophysiological data. As expected, a larger P3b ERP component was observed in response to attended infrequent events. Strenuous exercise did not differentially alter the amplitude or latency of the brain response during an attention task. This study reports a novel application of ERPs as a potential additional measure of the neurocognitive state that can be assessed on the sideline of a sporting event.