Help W/o touching the back button, it returns to the prevous screen?

[NewbieQuestion]

This has happened in the past, but not as much as it has lately. I won't even be touching the screen or any of the buttons at the bottom (the menu, the home, or the back button) and the screen goes back the previous one (on the internet or from a message to list of messages, to the home screen).

What do I do to prevent this from happening? Did I fry my circuit board? I'm still under warranty, can I get this covered?