Activated carbons are porous materials with a high surface area which are widely used in gases separation and catalysis. This work focuses on the understanding of the separation characteristics of activated carbons for purifying hydrogen from the wet mixture of hydrogen and carbon monoxide (in hundreds of ppm). This study would build a basic insight of the separation mechanism of the activated carbon and determine whether activated carbons are suitable for CO removal from the mixture. Systematic Grand Canonical Monte Carlo (GCMC) simulations have been carried out to assess the adsorption properties and selectivity of the activated carbon to the gaseous mixture with different gas phase compositions, temperatures, and pressures. The calculated adsorption isotherms, both for single and multi-component gas mixture, and isosteric heats of adsorption on the activated carbon showed reasonably good agreement with the experimental data available in the literature.