Type A-B differences were assessed measuring the P300 component of the event-related brain potentials that could reflect the resource demands of cognitive processings. Type A (9 females) and Type B (3 males and 6 females) students performed concurrently the reaction time (RT) and mental counting tasks. The dual task consisted of four conditions differing in task difficulty. The main results were as follows: Type A subjects performed no better on either task of the dual workload than type B subjects. However, Type A subjects showed higher subjective evaluation with NASA-Task Load Index than Type B subjects for each of the experimental conditions. Moreover, Type A subjects demonstrated greater amplitude of the P300 component for the RT targets all through the conditions than Type B subjects. Type A people's use of many resources in task performance seems to be associated with their hyperresponsivity in autonomic activities during mental workload that is known as a characteristic of Type A person.