Electrokinetic transport phenomena and slippage of fluid at the surface are often considered independently for description of microchannel flow. Anomalous cases of experimental results disagreeing with theoretical prediction have frequently been reported. By combining the electrokinetic effect and Navier's slip condition, we illustrate a possible explanation and present an analytical solution for oscillating flow in a circular microchannel. The derived analytical solution is useful for more general time-dependent problems through superposition of time-harmonic solutions weighted by appropriate Fourier coefficients. Our parametric results suggest that these two surface phenomena can be important for a better understanding of microfluid flow with hydrophobic channel walls.