Santa Monica police Sgt. Richard Lewis says Redmond O'Neal was pulled over about 8:30 a.m. Tuesday after an officer saw him fail to stop for a red light. Police say a search of his car uncovered the drug.
O'Neal, who is on probation in a previous drug case, was jailed without bail.
His lawyer, Richard Pintal, declined to comment.
The 26-year-old has a history of substance abuse problems. He completed a drug diversion program last year but remains on probation for bringing drugs to a Los Angeles County jail in 2009.
Tuesday's arrest was first reported by the website RadarOnline.com.