Self-activation takes advantage of the gases emitted from the pyrolysis process of biomass to activate the converted carbon, so that a high performance activated carbon is obtained. Kenaf fiber, one type of biomass, was self-activated into activated carbon. The Brunauer–Emmett–Teller (BET) specific surface area (SABET) of non-activation and self-activation pyrolyzed at 1100°C for 2 hours were analyzed and obtained as 252 m2/g and 1,280 m2/g, respectively, with 408% difference. The results showed that the highest SABET (1,616 m2/g) was achieved when a kenaf fiber was pyrolyzed at 1,000°C for 15 hours. A linear relationship was shown between the ln(SABET) and the yield of kenaf fiber based activated carbon through the self-activation process. The study also showed that a yield of 9.0% gave the highest surface area by gram kenaf fiber (80 m2 per gram kenaf fiber), and the yields between 7.2 – 13.8% produced a surface area per gram kenaf fiber that was higher than 95% of the maximum surface area by gram kenaf fiber.