A new form of nanofibre web electrode has been fabricated for a supercapacitor using electrospun polybenzimidazol (PBI)-based activated carbon nanofibres. A PBI solution in dimethyl acetamide (DMAc) is electrospun to a fibre web that consists of 250nm ultra-fine fibres. The web is successfully activated by steam of 30vol.% and the specific surface area of the activated web is in the range of 500–1220m2 g−1. The electrochemical properties of electrodes and the capacitive behaviour of the resulting capacitors are systematically studied using cyclic voltammetry, ac impedance and constant-current discharge tests. The specific capacitance ranges from 35 to 202Fg−1, depending on the activation temperature. The nanofibre web activated at 800°C exhibits the largest specific surface area and results in the highest capacitance. The capacitance of the electrical double-layer capacitor is strongly dependent on the specific surface area, pore volume, and resistivity of the samples.