Combustion in porous media has obtained a significant amount of attention within recent decades by offering several advantages cannot be achieved in conventional free flame burners. Lower pollutant emissions, higher flammability limits and better flame stabilization are some examples of these advantages. This work presents a computational study on the premixed combustion of a methane/air mixture in a porous medium burner. The porous medium comprised of two sections: the upstream one was labeled the preheating section and the downstream one was labeled the combustion section. GRI 3 reaction mechanism including 53 species and 325 reactions was used for methane oxidation. The model was validated against published experimental and numerical data. Conducting a baseline study, it was found that in a portion of the preheating section, porous medium gained higher temperature than the gas phase whereas it was vice versa throughout the combustion section. Moreover, it was noted that although CO concentration attained its peak at the flame front, NO concentration reached its peak at the burner exit. A stability analysis illustrated that interface of the two porous sections was a location at which flame could stabilize for a range of equivalence ratios. A parametric study revealed that as the mixture equivalence ratio ranged from 0.75 to 1.25, CO emission monotonically increased while NO emission first increased and reached its maximum for the stoichiometric mixture then decreased as the mixture became fuel-rich. Investigation of the porous medium extinction coefficient showed that larger extinction coefficients reduced the burner emissions.