A new Carrier Frequency Offset (CFO) estimation algorithm for IEEE 802.11a system is proposed. The extended Kalman filter (EKF) is applied to estimate the frequency offset in the acquisition stage and the cyclic prefix (CP) is used to correct the residual CFO in the tracking stage. Simulation results demonstrate the super performance of the proposed algorithm compared to Maximum-Likelihood (ML) approach. A new Carrier Frequency Offset (CFO) estimation algorithm for IEEE 802.11a system is proposed. The extended Kalman filter (EKF) is applied to estimate the frequency offset in the acquisition stage and the cyclic prefix (CP) is used to correct the residual CFO in the tracking stage. Simulation results demonstrate the super performance of the proposed algorithm compared to Maximum-Likelihood (ML) approach.