Hi,

No. There is no such examination which you can apply for while you are still in your 12th standard.There are definitely a few exams which you can sit for once you have passed your 12th boards.

National Defence Academy Examination(NDA)

A National Defence Academy is an academy of Indian Armed Forces, where cadets of the three services Indian Army , Indian navy and Indian Air Force are trained together before they go to final services academies. NDA was established in 7th December 1954.

Most of the other exams has set an eligiiblity criteria in which an aspirant must complete graduation before applying for the position.

Hope this helps!