Hey,
I assume you are using the stock model (reference card) it is a bit higher than most cards i have seen, but it is still within a more or less safe range. Running a stress test these cards heat up to about 77-80+C, however while gaming it should be lower, so yours is a bit hot. I believe it is still within range, keep the temps under 90C, however your temps should be lower. Most cards of the gtx500 series I have seen run a bit cooler, but fermi cards (gtx 400's, 500's) are known to run a bit hot.
How is your case cooling? Is your case large? How many fans?
Is your GPU overclocked? Is your fan set on AUTO, try upping the fan speeds in manual mode, but be careful not to accidently turn off the fan or set a low fan speed.
Hope this helps!