Abstract Aiming to add value to the ever‐increasing amount of residues from the palm oil industry around the world, lignocellulosic waste from palm oil (Lp) was used in this study to prepare activated carbons (ACLp) by chemical activation using KOH at 700 °C developing an area up to 1683 m 2 g −1 , this value was higher than that obtained for a sample of activated carbon prepared from commercial lignin (ACLc) of 588 m 2 g −1 . The activated carbons were deeply characterized by different techniques as SEM, FTIR, TGA, and nitrogen adsorption isotherms. The adsorption capacity of the obtained activated carbons for methylene blue (MB) was assessed. According to the results of the mathematical fits performed to the adsorption process, the adsorption isotherm showed a better fit to the Langmuir‐Freundlich model, with a maximum adsorption capacity of 188 and 51 mg g −1 for ACLp and ACLc respectively. In addition, its adsorption kinetics was found to fit better to the pseudo‐second‐order kinetic model. Additionally, the ΔG 0 value was lower for ACLp (−31 KJ mol −1 ) than for ACLc (−26 KJ mol −1 ) showing that the interaction between the MB and ACLp is more favorable.