Issue locking up?

[Hypo Luxa]

I've had my phone completely lock up on me a couple times, like the screen freezes and none of the hard buttons work... I can't even shut it down. I end up having to do a battery pull. Anyone else run into this? It's only happened like 4 times in the month and a half I've had it.

 

[ABRMess006]

This just happened to me for the first time the other night watching youtube, but that's it, haven't had a single issue other than that. Not too sure what is causing the problem though.