This paper evaluates the performance of a pilot-assisted fine carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) in time-varying channels. An analytical closed-form expression of the mean square error (MSE), of the post-FFT based CFO synchronization scheme, is presented in terms of time-variant fading channels. To verify our analysis in this paper, simulations are carried out within the framework of mobile WiMAX systems.