In this study, we used a two-stage process and potassium hydroxide (KOH) to transform waste biomass (rice straw) into activated carbon and then evaluated the adsorption capacity of the waste for removing bisphenol A (BPA) from an aqueous solution. Activated carbon removed BPA rapidly and effectively because of its high surface area and an adsorptive capacity (181.19 mg/g) that is significantly higher than many other adsorbents that have been developed in the recent past. The native and BPA-loaded adsorbents were characterized by scanning electron microscopy, elemental analysis, and Fourier transform infrared. Different adsorption parameters, such as the initial BPA concentration, contact time, temperature, and pH for BPA adsorption, were studied using a batch system. Equilibrium adsorption isotherms (Langmuir, Freundlich, and Temkin) and kinetics were investigated. The Langmuir model fits the experimental results well, compared to the Freundlich and Temkin models, and a pseudo-second-order equation was successfully used to describe the results of the kinetic studies. This study demonstrates that activated carbon produced from rice straw can be very effective in the adsorption of BPA from aqueous solution.