I/Q processing structures widely used in today's communication receivers, such as the low-IF and direct conversion architecture, face serious problem of I/Q mismatch. In practice, due to the problem of analog part, such mismatch is unavoidable, which results in finite and insufficient rejection of the image signal. These effects cause the desired signal to be interfered by image signal. In this paper, we focus on the low-IF receiver based on OFDM technique as today's popular transmission method. So, we carried out signal analysis and effects of mismatched I/Q processing in the OFDM low-IF receiver. Also, we proposed a new scheme that can compensate I/Q mismatch by least squares method using null-carriers of OFDM symbol. And, the computer simulation results are provided in order to evaluate the performance of the proposed schemes. From the simulation results, the mismatch problem could be perfectly compensated by using only one OFDM symbol.