The purpose of this study was to examine the influence of comfortable walking on brain activity during a working memory task using multiple psychophysiological evaluations. We used the Roken Arousal Scale as a subjective evaluation, and electroencephalograms (alpha attenuation coefficient (AAC), θFz/αPz) and near-infrared spectroscopy (oxygenated hemoglobin) as physiological indices. AAC is an evaluation index of arousal level, and θFz/αPz is an evaluation index of concentration power. To determine the comfortable walking speed for each participant, we used a 10-m walking test. The oxygenated hemoglobin concentration, AAC, and θFz/αPz value tended to increase with walking at a comfortable speed at the time of the working memory task. In conclusion, when comfortably walking while performing a working memory task, the decrease in the brain's arousal level is suppressed, and working memory ability and concentration are maintained.