Why is my S5 active randomly taking me back when I haven't pushed to back button?

[AC Question]

I can't use my phone! Every time I open something, it exits back to the previous screen, even though I didn't push the back button. It even makes the corresponding noise. I don't even have to be touching it. It isn't a set amount of time either. Could be two seconds could be thirty.

 

[B. Diddy]

Welcome to Android Central! The button might be faulty. Does this persist after reboot/ Try also booting into Safe Mode, to see if a 3rd party app is responsible: https://support.t-mobile.com/docs/DOC-10696