Coal, an industrial waste generated from an Algerian petrochemical industry was treated with NaOH and activated under microwave radiation to prepare low cost activated carbon. Effects of some operating parameters on the adsorption capacity of the prepared activated carbon were investigated. Results showed that the optimum conditions were as follows: impregnation time of 12 h, the impregnation ratio of NaOH was 0.4 g.g-1, microwave radiation time of 10 min and microwave power of 400 W. The prepared adsorbent was evaluated as an adsorbent for removal of methylene blue and methyl orange from aqueous solutions. The isotherm data could be well described by the Langmuir equation. pHpzc and FTIR characterization results of the prepared material showed that treatment increases the basic character of the activated carbon and promotes the adsorption of methylene blue dyes on its face.