Compressing files with WinRar command-line - files in use

I am using this simple command to zip files into an archive with WinRar. ``` winrar a -afzip -ep1 "C:\ok.zip" "C:\ok" ``` But if something is running (for example a simple .exe) from that directory it gives me error: "The process cannot access the file because it is being used by another process." Is there any switch that would compress even the files in use. I am sticking with WinRar as my customer has recommended it. But would like your recommendations too, but don't think customer is going to let me use anything else.