With aid of the recent development of computers, various direct numerical simulations (DNS) of turbulence are performed. Although the turbulence itself is unsteady in nature, the mean flow is assumed steady in most of the DNS's. This is because the DNS of the turbulence with an unsteady mean flow requires more computational effort to obtain a stable statistical averaged quantities. In the present study, a temporally sinusoidal pressure gradient is imposed on the turbulent channel flow. The each sinusoidal period is divided into a number of phases and statistical average is obtained for various turbulence quantities.