You Are Always IN/ON My Mind..??

I know we normally say “on my mind” but is it wrong to say “in my mind?” – LP

It depends on what you mean. When you say “There’s something on my mind.” you mean you are thinking a lot about that something or worrying about it. But when you say “I can still hear the music in my mind, even though the concert took place many days ago.”, you are talking about something you can still remember. “On someone’s mind” is an idiomatic expression: you can change “someone’s” to “my” or “your”, etc, but you can’t change “on” to “in” without altering the meaning of the expression

By FADZILAH AMIN - THE STAR