The electrochemical behavior of alkali-treated soft carbon (ASC) has been investigated in organic electrolyte solutions with different compositions. So-called electrochemical activation phenomena, in which higher capacitive currents are observed after certain anodic or cathodic polarization in the electrolyte solutions, depended on the electrolyte composition as well as its polarization condition. The anodic polarization in tetraethylammonium tetrafuruoroborate (TEABF4) solutions induced higher capacitive currents in the positive potential region where the electrochemical adsorption/desorption of anion acts as a charge compensation process, while the activation by cathodic polarization in TEABF4 solutions increased the capacitive currents associated with the cation adsorption/desorption. The electrolyte solvent also affected the activation process, especially for the cathodic activation. Larger sizes of ions and solvent molecules were generally effective for the activation, while the smaller sizes of them were preferable to obtain higher capacitance for the resulting electrochemically activated carbon.