Several high accuracy finite-difference time-domain (FDTD) methods have been developed to overcome the phase velocity errors present in the FDTD method. The nonstandard FDTD method has been developed as one of those. The phase velocity errors of the method are investigated and the characteristics are compared with other high-accuracy FDTD methods. As a result, the numerical dispersion characteristics of the method are clearly shown and the extremely high-accuracy characteristic at the desired frequency is confirmed.