Error deleting files and folders: File is in use

Hi, My computer hard drive free space is now very low, so I decided to remove useless files, I encountered an error when I want to delete a certain folder, the error message is telling me that it the file is in used, I posted below the exact error message.
Error Deleting File or Folder
Cannot delete test: It is being used by another person or program.
Close any programs that might be using the file and try again.
I check on the error message, I am wondering why I cannot delete the files, since I am not using the folder that I want to delete, I check on some viruses that might infect the folder, but none was found according to my anti virus application, please help me find ways on my issue, so that I can delete the folder, thanks a lot.
