The actor says he's contracted COVID-19, and he's placed himself in self-quarantine. Actually, Idris says he's been on lockdown since Friday. What's interesting about his case is he says he wasn't experiencing ANY symptoms.

Idris says, "I got tested because I realized I was exposed to someone who had also tested positive." He says he's quarantining for now with his wife, Sabrina ... although she hasn't been tested.

He added, "There are people out there who aren't showing symptoms and that can easily spread it ... this is real."

You'll recall, when Tom Hanks announced last week he and Rita Wilson had tested positive ... he said they at least had some indication -- body aches and other common cold-like symptoms.

No such warnings for Idris ... but he says, so far, he and Sabrina are feeling okay. Fingers crossed.