Why does my mobile blink off and turn itself on even though my application is still running?

[AC Question]

why my mobile used to blink off and turn itself on even though my application is still running

my mobile screen turn dark while using and turn itself on automatically.

 

[B. Diddy]

Welcome to Android Central! Which phone? How long does the screen turn off for? The phone isn't rebooting, right? Does this happen only with a certain app, or with any app?