A methanation catalyst, a carbon monoxide removing system, a fuel processor, and a fuel cell including the same, and more particularly a non-supported methanation catalyst including the catalytically active non-precious metal particles and the metal oxide particles, and a carbon monoxide removing system, a fuel processor, and a fuel cell including the same. The methanation catalyst has high selectivity for the methanation of carbon monoxide instead of the methanation of carbon dioxide and the reverse water gas shift reaction of carbon dioxide, which are side reactions of the methanation of carbon monoxide, maintains high concentration of generated hydrogen as small amounts of hydrogen and carbon dioxide are consumed, and effectively removes carbon monoxide at low operating temperatures of 200° C. or less.