This study presents a novel approach for effectively removing amoxicillin (AMX) from waste coffee grounds (CGs) using eco-friendly activated biochar-based adsorbents. To avoid the use of toxic chemicals, the adsorbents, called ACGs (activated CGs), were prepared by a water washing method followed by KOH activation. The adsorption performance of the ACGs was evaluated using various parameters such as the Freundlich isotherm, Langmuir isotherm, adsorption density, and pseudo-second-order equation to determine their maximum adsorption capacity and kinetics. Among the ACGs tested, ACG-4a, activated with KOH after water washing, exhibited significantly higher adsorption capacity (740.7 mg/g) compared to ACG-4b, activated with KOH after NaOH washing (549.5 mg/g). The superior adsorption capacity of ACG-4a can be attributed to its specific surface area. Notably, the ACGs demonstrated the highest AMX-adsorbing capacity when compared to other adsorbents.