In this paper, we consider estimation and compensation of the I/Q imbalance generated by the direct-conversion receiver in orthogonal frequency division multiplexing (OFDM) systems. Two methods for I/Q imbalance compensation are proposed: the maximum-likelihood estimation (MLE)-based method and the least-square estimation (LSE)-based method. Computer simulations are conducted for comparisons of the performance. Effects of timing and frequency offsets on performance are also analyzed. The MLE-based method generally performs well even at low signal-to-noise ratio (SNR) and is robust against timing and frequency offsets. The LSE-based method outperforms the MLE-based method at higher SNR. Both methods are robust against different gain and phase imbalances.