Kareem Jamar scored 14 points, Mathias Ward scored 13 and Will Cherry finished with 11 points for the Grizzlies, who won their 10th game in a row.
Montana (21-6, 13-1) led by double figures most of the way and remained a half-game behind Weber State for the Big Sky Conference lead. The Grizzlies face the Wildcats Tuesday night in Missoula in the final game of the regular season.
Gabe Rogers led Northern Arizona (5-23, 1-14) with 18 points. The Lumberjacks (5-23, 1-14) have lost 15 in a row.