Droid Bionic screen won't auto shut off when plugged in My phones screen will remain backlit and on while plugged in after getting a text or something that would pop up.

Even if nothing popped up, if I just unlock it while plugged in, it will never re-lock on its own.

This wasn't always the case but I didn't notice it for a while and am not sure what might be causing it. Maybe a background app?

Works normally when not plugged in.
Check to see if "System Settings / Developer options / Stay awake" is checked.  It's intended to give exactly that behavior ("Screen will never sleep while charging").