I sometimes get "Hey, you look busy!" as they come into my office.

A couple of days ago, a coworker came in to chit-chat and I kind of stayed focused on my computer screen (while showing some modicum of politeness by saying "uh-huh" every once in a while while she talked). Eventually she said "wow, you're really busy, aren't you? What're you working on?"

I'm working from home today.