Reserve Tony Allen contributed 12 points while Victor Williams and Andre Williams each added 10 for Oklahoma State (21-8, 10-6). The Cowboys shot 52 percent.
McFarlin had 14 rebounds and Andre Williams eight as the Cowboys held a 44-40 edge on the boards.
Oklahoma State limited Texas A&M to 23 percent shooting in the first half and held a 32-17 lead at the break.
Bernard King scored 17 points and Andy Slocum added 10 off the bench for Texas A&M (14-13, 6-10).