The body was found on Wednesday, Macks Lesufi said in a statement.
“The forensic pathologists of both the department and SA Police Service are on site carrying out [an] investigation,” he said.
On Monday, 45 patients at the hospital were evacuated after the psychiatric ward caught fire.
The cause was not yet known.
The patients were transferred to three other hospitals in the area.
Police spokeswoman Colonel Ronel Otto said a forensic team would investigate the cause of the fire.