It's the thermostat in the cooling system that controls the engine temperature and they generally work at the specified temperature until they fail. (You'll know about it if it fails as that usually causes over-heating.) If your temperature gauge is the needle type, this might simply be ageing of the gauge. If it's a digital display, it could be that the sensor is ageing.
I'd just keep an eye on the situation as it doesn't seem to be posing a problem at the moment. If it gets worse, it's simple enough to put in a new thermostat, although some cars make it very difficult to get to the thermostat housing. A new thermostat isn't expensive, but you should get a new housing gasket as well so as to avoid leaks. Search for videos showing how to replace an engine thermostat for more info.