97 Accord over heats?

I have a 97 Honda Accord 4 cyl 2.2L 135k miles. When I drive the car after about 20 min the temp gauge goes almost hot. But if I rev the car up to 2-3k it cools down again. The fan runs when the car is turned on and when its turned off. I have plenty of antifreeze in the tank & the radiator. I don't know what could be the cause of any suggestions?