You are receiving this prompt because every time a page containing the editor is loaded, your browser will check if you have a compatible version of Java installed. If this is not the case, it will automatically propose a current version of Java for download. However, to ensure this can happen automatically, the installed version of Java is compared to the current version of Sun's Java, which will build up a HTTP connection, which in turn causes this dialog to appear.

You can however disable the automatic Java check. To do so, please use this edit-on Pro JavaScript API method:

eop.setJREAutoDownload(false);

Please note: This function has to be called before eop.loadEditor(); in your page.

For more information please review the edit-on Pro Integration Manual.