What kind of applications do you have on your Berry? Trace back your steps, when did you first start noticing it happen? Was it after installing anything, try to be specific...
Posted from my CrackBerry at wapforums.crackberry.com
I always have it in my pocket, but with nothing else in it. No keys or loose change. The on apps I have are Facebook, and ESPN. Nothing else, and I have had them on my phone from day one, and never ran into this problem till recently. I have only had the phone for a couple months.
I had a curve that had this habit, sometimes it would throw in a random restart for fun , and I solved it by wiping the device from the security menu. Have you tried wiping and starting fresh?