I see it often and it's just condensation. Sometimes people here panic over this but it normally appears on some engines, especially if the car's used for alot of short trip driving in colder weather.
Don't worry or think about spending money to try solving that as you'll not solve it unless you drive more.
A bad t-stat (if stuck opened) might cause it if the engine doesn't get to normal operating temp long enough to burn off the condensation.