Google crawls public Ning Networks along with most other websites on the internet.
If you don’t want any content on your Ning Network to appear in Google search results, the best thing to do is to make your network entirely private. To do this, change the “Who can view” setting for any feature you have created in the Site & Pages manager in your network dashboard to “Members” or any option other than “Everyone”. Click “Save” at the bottom of the page.
You can also Edit Your robots.txt File and specify certain directories for search bots to ignore
If you’d like to keep your Ning Network public but prevent Google from crawling it, you can ask them to to exclude your Ning Network. Go to the Google Webmaster help center and follow the instructions.