Gerald Shargel, Bynes' attorney, informed Manhattan Criminal Court Judge Diana Boyar of the "What a Girl Wants" star's status Thursday at a hearing in Bynes' bong-throwing case, the New York Post reported.
Bynes, 27, is accused of tossing the drug paraphernalia out of a 36th-floor window of her apartment last May. She was charged with tampering with evidence, reckless endangerment and possession of marijuana after the incident.
"She's in a hospital in California. It's uncertain when she will be released. Obviously she is being treated there," the Post reported Shargel said at Thursday's hearing. "We are in touch with the district attorney's office and we hope to resolve this by Dec 5."
Bynes' California lawyer Rich Hutton said Tuesday she is mentally unfit to stand trial for a drunken driving charge related to her April 2012 arrest in Los Angeles.
Hutton said the actress currently does not have the mental capacity to understand the legal proceedings.
The judge in that case transferred the matter to a mental health court, which will conduct a hearing to determine Bynes' mental competency.
Bynes has been hospitalized for an undisclosed mental illness since July.
The former child star was placed on an involuntary psychiatric hold after she allegedly caused a disturbance when she tried to break into a retirement community in her hometown of Thousand Oaks, Calif.
The following night, she allegedly set a small fire in a driveway, which led to police involvement and her eventual hospitalization.
The actress is known for her work on TV's "What I Like About You" and "The Amanda Show," as well as in the film "Hairspray." Her most recent major screen credit was a supporting role in 2010's "Easy A," and her once-bright career has been eclipsed in recent years by her bizarre Twitter rants and frequent brushes with the law.