uh...so you think?
He had a lot on his mind
It is simply a warning to watch ("mind") where your head is so you don't bump it on something. You hear it when you are going through a short doorway, usually. Harkens back to a command to a ship's helmsman, "mind your heading" similar to "mind your helm". "Mind your head" is a shortened version.
What specific group do you have in mind?
person who is slow of mind
The mind is located in the brain. The brain is located in the head of a person or animal.
Ash is a crack head who bumped his head and Pokemon are in his mind as he is in a coma.
Chickens
The chorus to the song 'Over My Head' from the band The Fray is as follows:"And everyone knows I'm in over my head, over my head eight seconds left in overtime she's on your mind, she's on your mind."
When he opens his head and scratches his brain,you throw a grenade in his head
The song is from Fastball, It goes, Was I outta my head was I outta my mind how could I have ever been so blind I was waiting for an indication. Fastball Outta my head
A Mind to Kill - 1994 Head of the Valleys 2-5 is rated/received certificates of: Australia:M
"On my mind" means you are thinking of the person or thing, as if it were literally inside your head sitting on your mind.