Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
It's an animation/zoom thing. Similar types of things were present in iOS 7 for some people as well. Mainly depends on what apps you have on the screen you are unlocking to and their icon names and all that.
 
I did a video of a bug when unlocking my iPhone 5s with iOS 8, seems when there is one of those blue balls next to an app that has been updated it does a weird blue thing. See the video to see what I mean...

https://www.youtube.com/watch?v=5L1VWTk0vro

find a fix? I posted yest in the bug board about a weird phone icon zoom thing. from home screen open phone icon then quicky touch dial pad button and the phone icon zooms like over the numbers of keypad...very weird bug
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.