My American Green Tree Frog, Peeper, does this too. It's like GrifTheGrwat said, your frog is just scared. (S)he knows your not going to hurt him/her, (s)he just feel threaten because (s)he's small and your HUGEMONUS compared to him/her. So just deal with it and it may stop. Besides, your lucky! Peeper sometimes will poop and pee on me!