Are you using Disqus comment plugin for WordPress? The plugin generates a followed link Titled “blog comments powered by DISQUS”. If you want to nofollow the link follow the tutorial below
You have to edit the file disqus-comment-system/comments.php. I believe you have backed up the original file in case you make any mistake. Find the following code
Add rel=”nofollow” attribute for the link element. It should look like this
Now refresh the page you can see blog comments powered by Disqus link has become nofollowed. Happy SEO!