Ever since I came back to WoW for cataclysm I have had a problem with the auction house and I don't know whats causing it. Basically whenever I click on something, my dresser frame will come out and show the item (not a big problem here), but the weird part is, even if the item is not equip able (like a potion, scroll, gem etc.) the dresser frame will still come out and I get a message saying "I cannot equip that item". I have no addons that should mess with the auction house, but I will list them anyways and see if I can get any help.
The default AH interface (and all AH addons) has an option called "Show On Character", as Bendeis mentioned. You most likely turned on this option without realizing it - this option does cause the behaviour you're describing.