There are programs like 7zip (free) that you can use to extract the data from a rar-file. But that probably doesn't help to install it on your phone.
Let me ask: do you trust an antivirus made by a company that doesn't even know how to write installation instructions for their software?
Why not install an antivirus from the app shop from the maker? Apple has, Android has, Windows Phone has, Blackberry has.
Without knowing what antivirus (link please to the download site) and what phone you have your question, as can imagine, is impossible to answer.
i downloaded mobile antivirus,which is a rar file..i dont know how to extract/insert it into my mobile..