You are noticing that *.RBO files are constantly getting created in the ..\OfficeScan Client\Backup folder, consuming disk space. You want to know what these .RBO files are and if they are safe to delete.
These files are automatically created by the OSCE client as a backup after it tries cleaning infected files. To ensure that the user will a have a file copy in cases where the original file is damaged during the cleaning attempt, backup files are encrypted and stored in the \Backup directory of the OSCE client. Their file name extensions are also changed to *.RB0 - *.RB8.
You can safely delete these files if the cleaning attempt is successful.