Conversion of indigenous agricultural solid waste into high quality activated carbon was a multi-fold strategy to counteract two major environmental problems; pollutant agricultural solid waste open burning and a partial solution for high-cost coloured industry effluents treatment, particularly in textiles and food processing plants by offering low-cost activated carbon. In this study, coconut shells were physiochemically treated at high temperature (850°C) in the presence of potassium hydroxide (KOH) with 1:1 impregnation weight ratio and carbon dioxide (CO2) which acted as an oxidizing gas during activation stage. In order to evaluate the adsorption performance of prepared activated carbon (CS850A), a series of batch adsorption experiments were conducted at controlled parameters with initial concentrations of methylene blue ranging from 100 - 500 mg l^-1, temperature 30 ± 0.5°C, adsorbent loading 2.0 g and agitation speed of 100 RPM. It was found that the methylene blue adsorption on coconut shell-based activated carbon conformed to the Langmuir isotherm. The kinetic studies were well characterized by pseudo second order kinetic model. A suggestion has been made that the adsorption was favourable and was driven by a combination of physical and chemical adsorption forces. The monolayer adsorption capacity, Q0 was found to be 222.0 mg g^-1.