The anode electrode material is a crucial factor for the overall performance of a microbial fuel cell (MFC). In this study, a plain carbon paper modified with the CNT/MnO2 nanocomposite was used as the anode for the MFC and a mixed culture inoculum was used as the biocatalyst. The modified anode showed better electrochemical performance than that of plain carbon paper, and Brunauer Emmett Teller (BET) analysis showed the high surface area (94.6 m2/g) of the composite. The Mn4+ in the nanocomposite may enhance the electron transfer between the microorganisms and the anode material which facilitates electron conduction. Additionally, MnO2 can be used to store electrons due to its supercapacitance, which is comparable to that of the cytochromes present in the outer cell membranes of electrochemically active microorganisms. The MFC with a modified anode produced a maximum power density of 120±1.7 mW/m2, while the corresponding current density was 0.262±0.015 A/m2 at an external resistor of 800 Ω with an open circuit voltage (OCV) of 1.07±0.02 V. The unusually high OCV may be attributed to the high charge density developed on the bioanode by the charge accumulation in the MnO2 of the bioanode. This study showed that the CNT/MnO2 nanocomposite can be an excellent anode material for MFC.