Commercial carbon fiber paper (CFP) has been rarely used as an active electrode material for supercapacitors (SCs) due to its poor electrochemical activity and limited surface area. Herein, we report a facile, scalable and effective thermal oxidation method to directly activate CFP as a robust electrode material in SCs. Significantly, the activated CFP electrode exhibits a high areal capacitance of 0.75 F cm⁻² at 5 mA cm⁻² and excellent rate capability as well as cycling performance. Moreover, an advanced asymmetric supercapacitor (ASC) device with a remarkable energy density of 2.3 mW h cm⁻³ and outstanding long-term durability is achieved based on the as-obtained activated CFP electrode as the anode.