IXL Exhaust Fan turn on by itself

Hi All, we have an old IXL heat lap and exhaust fan in our ensuite. The heat lamps and exhaust fan is on 2 separate wall switches. Today the exhaust fan turned on by itself even if the wall switches are off. What can I do about this? I can turned it off unless I turn off the light switch at the electric board. Its 40 degrees today. Is that related? Thanks