Forte, a sixth-year senior, shot 4 of 9 from 3-point range to become just the seventh Big 12 player ever to reach 300 made 3-pointers. He also broke the Oklahoma State school record of 299 set by Keiton Page from 2008-12.
Jawun Evans added 16 points, seven rebounds and eight assists for the Cowboys (13-8), who won their third straight after a six-game losing streak.
Jaylen Barford scored 21 points to lead Arkansas (16-5), which saw its four-game winning streak snapped.
Oklahoma State started quickly, amassing early leads of 9-0 and 14-2, while the Razorbacks missed their first four shots and five of their first six.
Arkansas pulled within 25-17 with 10:20 left in the opening half, but the Cowboys went on an 18-5 run over the next five-plus minutes to push the advantage over 20. Oklahoma State led 59-33 at halftime.