my headlights started coming on when not turned on

why would it start doing this, would it be an expensive fix? The past couple of days while going to feed my horse ....going up the incline my fog lamp indicator flickered on and off a couple of times. Then I noticed coming in my driveway that my headlights are on and I hadn't turned them on. The switch is still in the off position. It's never done this before and no other signs. When I seen the fog light indicator is the first time.