There is an exclamation mark on the journal, in the duels category, but i have no achievments to claim. It has been there since about the patch that made duels not freeze when you tried to play it.
I also have an exclamation mark on my journal but none of my achievements clear the notification. Mine is under Gameplay - Alterac Valley. I’ve tried clicking on every achievement to see if it would clear the notification, but that doesn’t clear it. I think this bug appeared after playing a ranked match using a Mage or Priest deck (I forget which).
Edit: Ah! I just realized it’s going to be fixed in an upcoming patch: