With the increasing demand of wireless applications, current radio transceivers are challenged by the requirement of high data rate and high flexibility. Full-Duplex Dual-Band OFDM radio transceiver is a very promising radio technique to approach this goal. However, the mutual undesirable signal leakages due to the I/Q imbalance in the Full-Duplex Dual-Band RF front-end lead to a significant performance degradation in the radio link. In this paper, a practical and suitable digital I/Q imbalance estimation and compensation method for mitigating the I/Q imbalance in this flexible radio transceivers is developed and evaluated. The developed I/Q imbalance estimation method is based on the character of the frequency-flat-fading of the self-interference channel. The ADS-Matlab co-simulation results show that the developed digital compensation method can significantly reduce the impact of the I/Q imbalance on the Full-Duplex Dual-Band OFDM radio receivers.