on (one's) mind

Said when one is thinking, perhaps excessively, about someone or something. Jennie's been on my mind lately—do you know how she is? You look worried—what's on your mind?

on one's mind

Fig. occupying one's thoughts; currently being thought about. You've been on my mind all day. Do you have something on your mind? You look so serious.

on one's mind

Also, on the brain. In one's thoughts, preoccupying one. For example, The book prize has been on my mind, but I haven't been able to discuss it with you. It is often put as have something on one's mind (or the brain) meaning "be preoccupied with something," as in I didn't mean to be rude; I just have a lot on my mind right now, or John has nothing but girls on the brain. [Mid-1800s]