Locklear was pulled over while driving in the Santa Barbara area.
Law enforcement officers tell us alcohol was not involved, but they are conducting tests to determine if Locklear was under the influence of drugs.
We're told she was released on her own recognizance, without having to post bail.
This could set up a bizarre custody battle given that Locklear and ex-hubby Richie Sambora have both been busted for similar charges.
Sambora pleaded no contest to DUI back in March -- his daughter Ava was in the car at the time he was popped. We're told Heather's kid was not in the car when she was arrested.
In June, Heather checked herself into an Arizona medical facility to fight anxiety and depression.