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When it comes to operational human factors studies, the use of a number of different means (psychophysiological, questionnaires, performance indexes) to complete expert behavioral observations allows specialists to issue practical recommendations despite of the variability of the few operators involved. When it comes to mental workload, literature has identified several different physiological ways to assess it. We used Heart Rate Variability (HRV) and pupillometry for previous works (ISAP’11, ’13) and both have strong limitations: HRV can only be analyzed over 5-minutes time periods and pupil dilation is subject to light variability. During this study, we tested the electroencephalography B-Alert X10 system (Advance Brain Monitoring, Inc.) mental workload metrics. We set up an experiment on a video game in real life conditions in order to evaluate the reliability of this index. Participants were asked to play a video game with different levels of goal (easy vs. hard) as we measured subjective, behavioral and physiological indexes (B-Alert mental workload index, pupillometry) of mental workload. Our results indicate that, although most of the measure point toward the same direction, the B-Alert metrics fails to give a clear indication of the mental workload state of the participants. The use of the B-Alert workload index alone is not accurate enough to assess an operator mental workload condition with certainty. Further evaluations of this measure need to be done. As we observed in a previous study, pupil dilation is a reliable index of mental workload as it correlates significantly with most measures.