Biogas is an important renewable and clean biofuel. It is produced from the fermentation of biomass under anaerobic conditions and, thus, it is a renewable source of methane. Biogas refining according to national regulations standard produces biomethane, an alternative to natural gas. An important section of upgrading biogas to biomethane is CO2 removal. A technique commercially applied for this separation is Pressure Swing Adsorption (PSA). Activated carbons (AC) are frequently used for this purpose and modeling its CO2 adsorption equilibrium provides insights related to the interaction between adsorbate and adsorbent. Hence, equilibrium CO2 isotherm for a modified activated carbon was adjusted to Linear, Freundlich, Langmuir, Sips and Toth models and its CO2 adsorption capacity was compared to the literature results.