The temperature at which tuna is cooked will depend on a few different factors, including the size and overall thickness of the tuna you are cooking. Typically when tuna is baked or grilled it should be done so at a rather high temperature in order to avoid problems with bacterial infections in the meat. Since the last thing you will want to have to deal with is food poisoning, it will be extremely important to make sure that you cook it all the way through.
There are different ways of cooking tuna just like there is with beef. Some people enjoy their tuna to be cooked rare while other prefer it medium-well. The temperature that you cook your tuna at will vary depending on a few different factors, so keep in mind the thickness of your tuna before setting a certain temperature to cook it at.