Supercapacitors are promising energy storage devices due to their high power density, long cycling life, and short charging time. NiO is one of the alternative inorganic materials that could be used to replace the conventional RuO2 electrodes in these supercapacitors. In the present study, NiO thin film was prepared by radio frequency magnetron sputtering using a NiO alloy target. This process offeres several advantages such as the superior adhesion of the resulting thin films and the easy control of the deposition rate. Rapid thermal annealing (RTA) at different annealing temperatures was used to control the properties of the NiO thin films intended for supercapacitor applications. The lattice imperfections and interstitials/vacancies in the NiO thin films were influenced by the annealing temperature, and subsequently affected the bandgaps, optical transmittance, carrier concentration, and resistivity. Consequently, the the supercapacitive behavior was influenced by the surface area and the variation on the homogeneity of the crystallites in the NiO thin films with a change in the annealing temperature.