Bynes, 28, who has become known in recent years more for her legal woes and bizarre public behavior than her acting, was placed under so-called involuntary psychiatric hold after arriving in Los Angeles, her family's attorney Tamar Arminak said.
Under Californian law a person may be detained for mental health evaluation for up to 72 hours.
The development comes just hours after the actress accused (of a crime) that her father had fondled himself in front of her and asked her for sex. Later, she tweeted a withdrawal, blaming the comments on a "microchip" in her head.
"My dad never did any of those things. The microchip in my brain made me say those things but he's the one that ordered them to microchip me," she tweeted.
Bynes, who became a star at the age of 13 when she had her own comedy show on the Nickelodeon television network, has previously been placed under psychiatric care after she (claimed to be) started a small fire in front of a Los Angeles home.
Last Sunday, she was arrested on a crime charge of driving under the influence of drugs in Los Angeles, the California Highway Patrol said. She was later released from Los Angeles jail after posting $15,000 bail, according to jail records.
Bynes is also on three years' probation after pleading no contest in February to a separate crime charge of careless and dangerous driving with an alcohol part-related coming from/caused by a 2012 event when her BMW swiped the side of a patrol car in West Hollywood.
A case against Bynes for possessing marijuana and throwing a bong out of an apartment window last year was dismissed in June by a New York judge.