Little scab on mole

I have a little mole on my arm, a couple of months ago I noticed what looked like a little scab on it but after a week it fell off like a normal scab would do, I didn't remember hurting myself at all. I have just noticed it again on the same mole in roughly the same place and again I haven't hurt myself. I'm a little concerned now that maybe this is a sign of something more serious?