/wp-admin/admin-ajax.php is the callback file for the WordPress Ajax API. I am assuming, but I am fairly confident, that your plugin is using that API (as it should be). It isn’t an issue. You have to have an AJAX call load some file. WordPress just standardized that location. Despite its location in /wp-admin that same file is used by both front end, no-priviledge AJAX and logged-in user admin AJAX.
