Spokeswoman Alla Plotkin said her doctors recommended the elective procedure after monitoring the tumor "for years."
The elective procedure was to remove a meningioma, a slow-growing tumor in the membranes that cover the brain. Meningiomas usually occur in older adults and are mostly benign.
"It's not actually in the brain substance itself, it's a tumor that forms on the lining around the brain and then can grow very slowly and compress the brain and cause symptoms over a long period of time," said Dr. Paul G. Pagnini, M.D., director of clinical radiation oncology services at USC Norris Cancer Hospital.
Pagnini, who is not treating Moore, says the symptoms associated with meningiomas can be complicated.
"It could be something as just a headache that's just not going away and progressing over periods of time, and symptoms also location dependent so if it's pressing on structures in the motor cortex then a patient would develop some weakness in an arm or a leg," he said.
For most patients who undergo this procedure, the prognosis is good.
Moore was diagnosed with Type 1 diabetes when she was 33 and starring on "The Mary Tyler Moore Show." She appeared Thursday on the "Rachael Ray Show," taped on May 5, with former co-star Dick van Dyke.
The 74-year-old Moore gained stardom as a modern suburban housewife on the 1960s comedy "The Dick Van Dyke Show," then went on to headline her own successful series as a single woman pursuing a career.
The Associated Press contributed to this report.