Welcome to PS6Forums - The #1 PlayStation Forum. Why not take a minute to register for your own free account now? Registration is completely free and will enable the use of all site features including the ability to join in or create your own discussions.
Mine did this and had a right hissy fit a few weeks back.
The solution for me was to grab the disc and power off at the mains for 5 mins. After a reboot she has been fine for 2-3 weeks now.
There are a couple of potential causes from the software to the position of the eject button and even a possibility your manual eject screw could need tightening up.
I would say turn it off first as it could be a software error and something hasn't shut down properly.
If this doesn't work google "PS4 eject screw" (I can't post a link as am such a n00B!)
I now close the apps using the option button, eject the disc using the options and shut down (fingers crossed it works ok for you).