Nitrogen-enriched activated carbons were prepared from waste medium density fiberboard base using K2CO3 as an activating agent for electrochemical capacitors. The effect of different temperatures of carbonization (300, 400, 500, and 600°C) and the influence of the sequence of activation process (a mass K2CO3/coke ratio of 3, temperature of 800°C and the activation time 1h) on the electrochemical performance have been investigated. All of the samples were characterized in terms of surface chemical composition by elemental analysis and X-ray photoelectron spectroscopy, porosity by N2 sorption at 77K, surface area by Brunauer–Emmett–Teller measurement. Electrochemical behavior as electric double-layer capacitors was determined using galvanostatic, voltammetric charge/discharge, specific capacitance values versus current densities, and impedance spectroscopy techniques in a 7molL−1 KOH aqueous solution. A maximum value of specific capacitance of 230Fg−1 was achieved for the sample carbonized at 400°C. The good electrochemical performance of the activated carbon was ascribed to high surface area, wide pore size distribution, and the presence of nitrogen functional groups.