In this paper, we propose two methods to compensate the I/Q imbalance generated by the direct conversion receiver in orthogonal frequency division multiplexing (OFDM) systems. In our proposed methods, the channel is considered to be an unknown multipath channel with additive white Gaussian noise. 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 considered. We find that the MLE-based method generally performs well and is robust against timing and frequency offsets. The LSE-based method performs well at high signal-to-noise ratio and is robust against the timing offset.