Hi,
Unfortunately, without further details on your Specs etc... it would is too hard to diagnose the issue and if it is only dropping minimally then there should be no need to worry, also keep in mind the more software you are running on your computer the more resources the system will use. making that sudden drop in FPS.
But you can always try Iobits Game Booster to close any programs running in the background before playing and see if that helps