In this study, dynamical properties in brain activity have been analyzed by means of observed near infrared spectroscopy (NIRS) data at the area of brain of primary motor. Nonlinear properties are investigated by using the methods of delay vector variance (DVV) and data surrogate. The result shows that the underlying processes of the change of oxygenated-hemoglobin and deoxygenated-hemoglobin concentration are highly stochastic. The number of NIRS time series exhibiting nonlinearity in the task of imagery of movement is larger than that in the task of relax. In addition, the level of nonlinearity in such the dynamical processes is rather low.