"I began not to feel well. Nothing serious, just under the weather," she wrote Wednesday. "I contacted my doctors and flew back to NYC. They felt it best to admit me into the hospital for a few days. Seems my young immune system needed a little boost to fight off 'opportunistic infections.'"
Roberts, 52, returned to the anchor chair in late February, five months after undergoing a bone-marrow transplant. The breast cancer survivor had the bone-marrow transplant to treat myelodysplastic syndrome, a rare blood disorder.
She insisted last week's setback was minor and not surprising.
"My doctors assured me that this was NOT because I was working or doing too much, too soon," she wrote on Facebook. "It's extremely common, post bone marrow transplant, to have complications. I'm blessed that mine have not been severe."
Roberts said she expects to return to work next week.
Celebrity Families of 2014 [PHOTOS]