There is a way to save a copy of your web pages. If you open your site in Internet Explore, and click File > Save As > Web Page Complete, then it will create a folder for each page of your site.
Depending on the reason that you are wanting to make a copy, this may or may not work. The copy that you save would not serve as a good backup as it does not contain the associated .xpf file which is something that is generated by the SiteBuilder software and is converted to html.
In case you are wondering, we do nightly backups of all the sites that we host. Also, you do have the ability to create a copy of the site right in your account if you wish.