Recent fMRI studies of human motor function and learning have reported that the magnitude of brain activity involves a decreasing trend over repeated tasks in the absence of improvements in task performance, probably suggesting the effect of habituation. Here we show that similar effect can be detected by NIRS. In experiments, oxygenated hemoglobin (HbO) changes were monitored during a finger tapping task over repeated sessions. Results showed that task-related brain activity exhibited a decreasing trend on motor-related areas over the sessions. These suggest that measurements of NIRS may exhibit the brain-induced trends over repetition of simple motor tasks.