The increasing focus on environmental preservation and protection necessitates the development of new methods and technologies for treating various wastes (solid, liquid, and gaseous) generated by human activities. Adsorption using activated carbon materials offers a promising approach for removing pollutants like methylene blue from wastewater. This study aims to produce a carbon-rich adsorbent from a biomass source (date seeds) and transform it into activated biochar (ABC), as the impact of physicochemical parameters on the adsorption capacity, including temperature, mass loss during the activation (400 °C, 600 °C, 800 °C, and 1000 °C) for both sizes (1 mm and 250 μm), methylene blue concentration, adsorption time, and adsorbent Mass. Additionally, the activated biochar ‘s morphological structure and functional groups are characterized by SEM, XRD, and FTIR. The results demonstrate that the optimal activated biochar (ABC) is obtained at an activation temperature of 1000 °C. At this temperature, the yield (Y%) and adsorption capacity (qe) reach 99.15% and 19.83 mg/g, respectively. Conversely, the lowest yield (Y%) and adsorption capacity (qe) are observed at 400 °C, with 86.4% and 17.28 mg/g values, respectively. For a methylene blue concentration of 3.0 mg/L, the best yield remains at 99.12%, and the adsorption capacity is 19.82 mg/g. The effective adsorption time reached 60 minutes, corresponding to a yield of 96.16% and an adsorption capacity of 9.61 mg/g.