You are probably subscribed to that thread. Try going to that thread and at the top there is a tab labeled Thread Tools. I believe in that tab you can unsubscribe to the thread. This should stop the emails.
Also, go to your User Control Panel, this is at the top of any thread labeled User CP. Look for edit options and on that page there is a selection for thread subscriptions. Check the setting there, mine is Do Not Subscribe.
Hope this helps.