Thats totally normal, especially if you just got your betta less then a couple weeks ago. If I put my finger RIGHT up on the tank, all my boys will back away and stare at it(my braver ones might flare a bit), and my spaz/nutcase Smore will have himself a little heart attack
And I've had Smore for several months ;)
Though if hes hiding ALL the time and isn't a new betta(been with you for a month or more)Then the hiding may be a reason for concern.....but if hes fairly new, hes probably just getting used to his new home. If he really seems scared and skittish about EVERYTHING, maybe move him to a quieter location for a while and let him get settled.