This has started happening to me today too.
I have all of my followed blogs (except for one) set up so that I receive no post and no comment emails on all of them. I choose just to have any new post show up only in my reader.
I have clicked on the link (that csonnek advised above) to show if I am following any comments and it tells me that I am not.
The blog that is showing up comments in my reader is a blog I follow, but I have not followed any of the specific posts comments that are coming up.
The blog that I am receiving these comments on is mintedmoose.net
I have not tried the unsubscribe and resubscribe option - I would prefer to wait to hear from someone at WordPress if there is a slight glitch that needs fixing.
I look forward to hearing from you guys and hope you can help me too.