Reverse electrodialysis (RED) is an electrochemical process for converting salinity gradient energy into electric energy. Biofouling of anion exchange membranes (AEMs) is a severe problem affecting RED performance. In this study, we examined the biofouling of AEMs during RED and attempted to improve the anti-biofouling properties of AEMs through surface modification. Biofouling was evaluated from the bacterial coverage percentage, obtained from surface analysis using scanning electron microscope (SEM) images of fouled AEM surfaces. The results showed that a polydopamine (PDA) coating improved the anti-biofouling properties of AEM under RED operation. Furthermore, in order to investigate the effect of electric current and electric field, RED was performed under open circuit conditions (i.e., only an electric field was generated) in addition to normal RED, which generated both an electric current and an electric field. Both the generated electric current and the generated electric field suppressed bacterial attachment on the AEM surface, thereby enhancing the anti-biofouling properties of AEMs along with the PDA modification. It was also found that electric current changed the shape of bacteria.