Estimation of Carrier Frequency Offset (CFO) is the fundamental problem of OFDM systems. CFO can be estimated using either time domain or frequency domain methods. A comparative study among different methods of carrier frequency offset estimation in OFDM systems is presented. We consider two techniques in time domain, namely; the Cyclic Prefix (CP) method and the Training Sequence Method. In addition two techniques in frequency domain are considered, namely; Training Symbol method and Pilot Method. Mean square Error (MSE) is the comparison criteria used in the study. Simulation results show that the CFO estimation methods in frequency domain have better performance than CFO estimation methods in time domain, in terms of mean square error (MSE). It is shown that, the pilot tone method outperforms the cyclic prefix method by 7dB and the training sequence with two identical blocks by 10dB. The symbol based method outperforms the pilot tone method by approximately 2dB. The comparison results are considered at MSE of 10-4 and normalized CFO of 0.2