at a meeting和in a meeting都可以說，請看實例(大都出自權威詞書)：
Officially, the director is in a meeting, though actually he’s playing golf. 據說主任正在開會，可他實際上正打高爾夫球呢。——見《牛津高階英漢雙解詞典》(第四版) (officially詞條)
I’m tied up in a meeting until 3 pm. 我開會直到下午三點鐘方可脫身。——見《牛津高階英漢雙解詞典》(第四版) (tie詞條)
Sorry to keep you waiting—I got stuck in a meeting. ——見《朗文當代英語詞典》(1995年版) (keep詞條)
Mrs Lavelle is in a meeting at the moment. ——見《朗文當代英語詞典》(1995年版) (meeting詞條)
There were three others present at the meeting besides us. 除了我們之外，還有其他三人個出席了會議。——見《朗文多功能分類詞典》(besides詞條)
He took the chair at a meeting some time ago. 前些日子他主持了壹次會議。——見王福禎編著《新時代英語慣用法詞典》第195頁。
There were both blacks and whites at the meeting. 參加會議的有黑人也有白人。——見周貞雄編著《大學英語重點詞用法手冊》besides詞條)
She might be invited to speak at the meeting. 她可能被邀在會上發言。——見張道真編著《張道真英語語法》第116頁。