Estimation of pilot proficiency is important to provide efficient and effective training and to prevent flight accidents. We hypothesized that pilot proficiency could be estimated by assessing mental workload during flight training, and auditory steady-state response (ASSR), a kind of auditory evoked brain potential, could be an index of mental workload during flight training in a simulator, consequently, an index of pilot proficiency. A periodic sound induces ASSRs that have the peak frequency at the frequency of the sound, and reducing attention to the sound is known to decrease amplitudes of ASSRs. Then, when a task-irrelevant sound induced ASSRs during a task phase, such as takeoff or landing, in flight training, smaller ASSRs would indicate limited attention to the task-irrelevant sound and greater attention to the task. That is, smaller ASSRs could imply the workload was high. Thus, ASSRs during a task phase would be small when a pilot is a novice and become larger with the pilot getting trained. In this case, ASSRs could be used to estimate pilot proficiency. In this study, three participants with no flight experience underwent a series of simulator training sessions, each of that lasted approximately two hours. During taxing, takeoff , level flight and landing task phases in six training sessions, a task-irrelevant sound of the frequency of 40 Hz was presented and electroencephalogram (EEG) of each participant was recorded. The results showed that the ASSRs were getting larger with the participants experienced more training sessions. The results of this study indicate that ASSRs could be used to estimate pilot proficiency.