According to police, Clark, a freshman, was arrested, booked into the Edmund, Okla., jail and released after posting bail.
Clark was averaging 7.0 points and 3.7 assists as the backup to Marcus Smart.
Edmund police public information specialist Jennifer Monroe said Clark was arrested at 9:57 a.m., and was the passenger in a vehicle pulled over for a seatbelt violation. Clark and the driver were both arrested for possession of marijuana.
Clark was suspended for four games earlier this season, and a source close to the situation told ESPN.com the suspension was also marijuana-related.
The arrest comes one day after the Cowboys lost starting center Michael Cobbins for the season with a torn Achilles.
Oklahoma State is ranked sixth in the country and will face Kansas State on the road Saturday in the Big 12 opener.