Error deleting unknown files in use?

Curiosity takes my attention with these six files on my documents, I’m not familiar with these files, and I don’t even remember creating those files before. So, to clean up this mess I select those files and delete.
At first It asked me If I’m sure to delete this file and I hit yes, but instead of sending these files on bin it says it can’t be deleted because it is used? See.

This action can't be completed because the file is open in system.
I wonder how it is being used. Since I don’t have any open files before.
How to delete this files?
