The two worked together for the first time in the campus comedy 3 Idiots.
The actress told The Times of India: "Aamir takes a long time to make up his mind about projects.
"I keep telling him that by the time he decides to make this romantic film with me, my niece Samaira will be ready for stardom."
She also described her co-star as "chivalrous" because he stopped the shoot every time her make-up ran during a dance sequence in the rain.
Khan confirmed to the newspaper: "Bebo [Kareena] has been asking me to direct her in a romantic film... and I am definitely contemplating it."