In this work, cow manure (CM) was reused as a potential precursor in the production of activated carbon (AC) using a potassium hydroxide activation process at different temperatures (i.e., 500, 600 and 700 °C). The optimal activated carbon from cow manure (CM-AC) with high specific surface area (ca. 950 m2/g) was further investigated for its adsorption performance in the removal of a model compound (i.e., methylene blue) from aqueous solution with various initial concentrations and adsorbent dosages at 25 °C. It was found that the resulting AC could be an effective adsorbent for removal of cationic dye from aqueous solution in comparison with a commercial coal-based AC. Based on the observations of the energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy (FTIR), the CM-AC adsorbent has a stronger interaction with the cationic compound due to its more oxygen-containing complex on the surface. Furthermore, the adsorption kinetic parameters fitted using the pseudo-second order model with high correlations were in accordance with their pore properties.