The 33-year-old star has been dating fellow actor Kunal Khemu since 2009.
She told The Times of India: "I am not a responsible person. I am a child. I don't really feel like a grown-up and marriage is meant for mature people.
"The thought of marriage makes me weak. I think that 30 is the new 20. So, I am not tying the knot anytime soon."
The actress has previously denied that she is secretive about her relationship with Khemu.
In March, Khemu said that the two would not be following in the footsteps of Khan's older brother.
Saif Ali Khan announced his engagement to girlfriend Kareena Kapoor earlier this year.
However, the marriage has been postponed because Kapoor reportedly wants to concentrate on her career.