Carbon nanofibers (CNFs) are synthesized by pyrolysis of polyarylonitrile (PAN) nanofibers that are prepared by dissolving of PAN in N,N-dimethylformamide (DMF) solution followed by electrospinning and drying. The obtained CNFs are further treated via a CO₂ activation process. The morphology and porous structures of the obtained nanofibers are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂ sorption measurements. Effects of polymer solution concentration and static voltage during the electrospinning process on the morphology and diameter of nanofibers are studied. Their unique microstructural features enable the CNFs to present outstanding high specific capacitance in aqueous, non-aqueous and novel ionic liquid electrolytes. Moreover, the CO₂ activated carbon nanofibers (ACNFs) exhibit a high specific area (2866 m₂ g_-1) and pore volume which is almost three times higher than that of the raw carbon nanofibers. Overall, combinations of the high surface areas and outstanding electrical conductivity make the activated carbon nanofibers could have a further application in supercapacitor electrode materials.