Many chemical reactions that produce a wide range of hydrocarbons and alcohols involve the breaking of C-H bonds in methane. In this paper, we analyzed the decomposition of this molecule on the B5 step-edge type site of Ru surface using first principles calculations based on dispersion-corrected density functional theory. Methane was found to be weakly adsorbed on the surface, characterized by the hybridization of its sp states with Ru-d xz,yz,zz states. Dissociative adsorption is energetically preferred over molecular methane adsorption, resulting in CH fragment. CH is strongly adsorbed on the surface due to the prevalence of low-energy sp-d bonding interaction over the electron-unoccupied anti-bonding states. This highly stable CH requires higher activation barrier for C-H bond cleavage than CH4.