Here's a couple things.
1) how do you know that your room is 76 degrees?
2) what size is your tank?
3) does the tank get direct sunlight? is it directly under or next to a heating vent (assuming you are running your furnace?)
The reason I ask is because lights and pumps can easily add 100 watts to the heat in a tank. If you had a 55 gallon tank, and the room was really a little warmer (82 for example) the water could easily be 90 because a tank that size with 100 watts of auxiliary power can gain 8 degrees over ambient temperatures even without a heater.
Otoh, lets say the room is really 76. If the tank is near a heater and/or getting direct sunlight, it could again get to 90 because the lights and pump could get it to 84, while the sun and heater could do the rest.
And of course, it could be some combo of that. The room might go up to the low 80's during the day, and drop down later, while there is a secondary source of heat.
It it were me, I'd remove the heater and see what the temperature of the tank is in 24 hours. Given the circumstances, the tank could hardly drop below 80 even without a heater, so there's no obvious danger.