have somebody/something on the brain

have (someone or something) on the brain

To be thinking of someone repeatedly over a period of time; to have someone at the front of the mind. I had Alice on the brain today, and she just called me, can you believe it? Do you want Italian or Chinese tonight? I know dinner is hours away, but I just have food on the brain.
See also: brain, have, on
Farlex Dictionary of Idioms.

have something on the brain

be obsessed with something. informal
See also: brain, have, on, something
Farlex Partner Idioms Dictionary

have somebody/something on the ˈbrain

(informal) think and/or talk a lot or too much about somebody/something: You do nothing but talk about your job; you’ve got work on the brain!
See also: brain, have, on, somebody, something
Farlex Partner Idioms Dictionary

have something on the brain

tv. to be obsessed with something. (Have got can replace have.) I have money on the brain, I guess.
See also: brain, have, on, something
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • accompany (one) on a/(one's) journey
  • accompany on a journey
  • a stranger to (someone or something)
  • be out of (one's) league
  • be out of somebody's league
  • be in bad with (someone)
  • (one) puts (one's) pants on one leg at a time
  • bargain
  • bargain for (someone or something) with (someone)
  • brief (someone) about (someone or something)