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A supercapacitor is an energy-storage device able to store and release energy at fast rates with an extended cycle life; thus, it is used in various electrical appliances. Carbon materials prepared above 800 °C of activation temperatures are generally employed as an electrode material for supercapacitors. Herein, we report carbon materials prepared from a low-cost petroleum waste carbon precursor that was activated using KOH, MgO, and Ca(OH)2 only at 400 °C. Electrode materials using low-temperature activated carbons were prepared with commercial ink as a binder. The cyclic voltammetry and galvanostatic charge–discharge were employed for the electrochemical performance of the electrodes, and studied in a 3-electrode system in 1 M solutions of potassium nitrate (KNO3) as electrolyte; in addition, the supercapacitive performance was identified in a potential window range of 0.0–1.0 V. The best-performance activated carbon derived from vacuum residue with a specific surface area of 1250.6 m2/g exhibited a specific capacitance of 91.91 F/g.