Macbook Air early 2014 11 inch fan keeps running even when it doesn't need to

I have a Macbook Air, Early 2014, 11 inches. The fan keeps running even when the mac is cold. The weird part is that when I open the Macbook, for 20 seconds it is pretty fast, and not heating up. This is expected. But after 20 seconds the Mac's fan starts running for no apparent reason and the mac slows down a lot. Does anyone have an idea on how to fix this? Or should I just take it to the nearest Apple store and ask them what the problem is?