In the textile industry, several dyes are utilized for colouring fabric products. The amount of dye that is discarded from textile wastewater can range from 5% for basic dyes to 50% for reactive dyes, which can cause serious environmental impacts. This study focused on the bio-adsorption of reactive red dye on activated khat stem discharged as waste from consumers. The khat stem was carbonized and chemically activated using phosphoric acid to increase the surface area and surface reactivity. The prepared bio-adsorbent was characterized for its physical and chemical properties by applying proximate analyses, pHpzc, BET, FTIR, SEM, and XRD). Batch adsorption experiments were carried out in order to evaluate the removal efficiency of the specific dye and obtain the optimum removal conditions. Around 30 experimental runs were performed at different process variables like pH, adsorbent dose, contact time, and initial dye concentration designed by response surface methodology based on the Central Composite design, and the corresponding removal efficiency of the prepared bio-adsorbent. The removal efficiency was obtained in a range of (19.27-94.5)%. The optimal conditions for maximum removal efficiency of RRD (94.5 %) were observed at pH = 3.05, dose =1.05 grams, contact time =38.79 minutes, and an initial dye concentration of 50.4 mg/L. At this optimal condition, adsorption isotherm, adsorption kinetics, and adsorption thermodynamics were studied. The Languimer isotherm model and the Pusdo second order kinetic model well described the experimental data. These results suggest that activated khat stem material can be used as a promising bio-adsorbent for removing the reactive red dye in textile wastewater