Carbon nanofibers (CNFs) and MnO (X) @CNF nanocomposites (MCNFs) are fabricated by electrospinning and investigated as free-standing electrodes for supercapacitor. This work presents the effect of heating rate during carbonization on the electrochemical behavior of the as-prepared MCNFs electrodes in 6 mol/L KOH electrolyte. Results show that the MCNFs electrodes carbonized by relatively slower heating rate exhibit higher specific capacitance. The electronic conductivity of the slow heated MCNFs electrodes is better than that of the fast heated electrodes due to the better crystallinity of the MnO (X) nanoparticles and the graphitic carbon layers forming on the surface of the Mn-loaded CNFs. These MCNFs electrodes demonstrate elevated rate capability and improved cycling performance without adding any polymer binder or electronic conductor.