The purpose of this study was to investigate whether peppermint and orange reduce psychological stress and enhance concentration of attention during mental arithmetic. Ten male students participated in this study performed mental arithmetic test two times. We measured oxy-hemoglobin concentration in cerebral blood flow (ΔO₂Hb) in frontal and temporal lobes, blood pressure, and the number of answers and mental impressions for the test and presented aromas. The aromas and non-odor were presented during 9th minutes from beginning the test. Peppermint and orange remained and significantly increased ΔO₂Hb in left and right temporal lobes, respectively, while the aromas did not change the number of answers. Principle component analysis for mental state and behavioral data as well as for the measured all variables showed the aromas contribute to enhance concentration and inhibited sleepiness, and the aromas separated psycho-physiological response, respectively. The findings indicate that temporal aroma presentation mainly changes brain activity and thus improves concentration of attention.