In WLAN receivers, a direct conversion architecture has been implemented in recent years. Though this architecture reduces cost and power consumption, it may suffer from direct current (DC) offset and frequency offset. To reduce the effect of DC offset, a frequency offset estimation scheme with a differential filter for orthogonal frequency division multiplexing (OFDM) direct conversion receivers has been proposed. However, the receiver may also suffer from IQ imbalance, which deteriorates the performance of frequency offset estimation. In this paper, the performance analysis of the frequency offset estimation scheme with the differential filter in the presence of IQ imbalance is derived. The numerical results obtained through computer simulations show that the derived analysis provides close approximation to the performance of the frequency offset estimation scheme. It also clarifies the dependency of the mean square error on the waveform of the preamble symbols, which is caused by IQ imbalance.