Yes—just check the “block search engines” checkbox in the “Edit Contest” screen.

You might want to do this if you’re concerned about your contest appearing when people search for your brand or domain name.

After this option has been activated, we’ll ask the Googlebot, Yahoo’s Slurp spider, or any of their siblings to remove your contest from their indexes—this can take a while, so you’ll need to be patient to see it take effect.