Ventura County sheriff's Capt. Don Aguilar says deputies responding to a call Monday night found Bynes standing next to the flames in the city of Thousand Oaks.
The deputies determined she met the criteria for a mental health hold and took her into custody. She can be held for up to 72 hours of observation.
Aguilar says no charges have been filed.
The 27-year-old former Nickelodeon actress has had several run-ins with the law in California.