I've had that happen several times and resetting the Sim fixes it. Here's what you do:
Open the cheat/control window by holding down Ctrl, Shift, C. You'll know it's open because the screen becomes a little darker and you're able to type commands. Type in these words EXACTLY as they are typed here, except using your Sim's actual name. It's case sensitive.
resetSim Firstname Lastname
Then press Enter. This should reset your Sim and remove the object from his or her hand.
Let me know if it works.