In our competitive society, efficiency is of central concern. The pace of life is gradually becoming faster. Whether official business at the workplace or private business at home, we may face stress and be bothered with anxiety and emotionality. The result may cause physical and mental damage. The stress employees encounter at work may essentially endanger their health; moreover, it can induce human error that may cause an accident. Past research suggests 70% -90% of system failures result directly or indirectly from human error due to work stress. The result of stress may thus severely impair the system and the worker. The aim of this study was to investigate the relationship between different levels of time pressure and brain activities measured by fNIRS (functional near-infrared spectroscopy) and electroencephalogram (EEG). Ten university students participated as volunteer subjects in this study. The fNIRS results showed that brain activity significantly decreased with increasing time pressure in the frontal and left occipital areas; with increased time pressure, the control of blood vessels within the brain decreased. The EEG basic indices Ɵ and a at all recording sites presented to increased and decreased, respectively, with the level of time pressure. The index β tended to increase from time pressure level 1 to level 2, while decreasing from time pressure level 2 to level 3. This demonstrated that subjects failed to relax, got more tired, and appeared less attentive when facing high levels of time pressure. The amplitude of the ERP (event related potential) registered from the occipital lobe of participants decreased with time pressure. The results suggest that information processing ability is decreased under time pressure. NASA-Task Load Index (TLX) rating scales in three mental arithmetic tasks showed no significant differences, which suggests that subjective assessment via questionnaires is not sensitive for 250measurement of mental stress and reveals the valuable application of using physiological measurement.