Looking on the internet deeply has found these results:

at my office is the most popular phrase on the web.

in my office 1881,000 results on the web	at my office 116,510,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Jan 24, 2011 ... John could have said: "I left it in my office." To summarise, 'at' is a more general, vague term, whereas 'in' usually refers to a specific location. Dec 14, 2006 ... If I'm on the phone in my office, I would say, meet me in the office. If I'm on the ... And how to say "you can take it in my office\ at my office" ? Apr 30, 2015 ... I secretly lived in my office for 500 days. Unable to pay rent in L.A., I slept behind my desk. But what began as a quick financial fix soon became ... "Mr. Franklin," said Bill's boss sort of sternly, "Could I see you in my office for a minute? We need to talk about something." See also: could, see. McGraw Hill ...	It was around the time your friend Captain Raydor showed up at my office. Chloe showed up at my office here at JAG. Gerald Kozko was at my office today. You can call me at my office too. A boy who works at my office. I got a message at my office today from Sophia Russo. There's an opening at my office. I am getting you an interview at my office.

in my office

1881,000 results on the web

at my office

116,510,000,000 results on the web

More popular!

Jan 24, 2011 ... John could have said: "I left it in my office." To summarise, 'at' is a more general, vague term, whereas 'in' usually refers to a specific location.
Dec 14, 2006 ... If I'm on the phone in my office, I would say, meet me in the office. If I'm on the ... And how to say "you can take it in my office\ at my office" ?
Apr 30, 2015 ... I secretly lived in my office for 500 days. Unable to pay rent in L.A., I slept behind my desk. But what began as a quick financial fix soon became ...
"Mr. Franklin," said Bill's boss sort of sternly, "Could I see you in my office for a minute? We need to talk about something." See also: could, see. McGraw
Hill ...