PS3 trouble

Are you hitting the PS Home Button when you put it down or tapping the power button on the console again by accident?

If it seems like a persistent problem, I would see if your PS3's firmware is up to date, otherwise, you could always use the on/off switch in the back (this is in reference to the older PS3 models, I'm not sure if the Slim versions have those on the back, if not, unplug the cord).

The other thing that could be causing it is if you have other options checked to turn it on. Check your settings and turn remote play off and check to see if you have auto-update on.

If those don't work and it's still under warranty, I would call Sony and troubleshoot with them and then send it in if you need to. You could also take it to a local game/computer store that fixes consoles.