Yes, you need to bring OBC certificate for age relaxation in the IAS exam. It will be very helpful for you in getting the age relaxation.

Age limit:
A candidate must have attained the age of 21 years and must not have attained the age of 32 years on 1st August, 2014

Relaxation upto 3 years for OBC
Relaxation upto 5 years for SC/st

Nationality:
A citizen of India, or
A subject of Nepal, or
A subject of Bhutan, or
A Tibetan refugee who came over to India before 1st January, 1962 with the intention of permanently settling in India, or
A person of Indian origin who has migrated from Pakistan, Burma, Sri Lanka, East African countries of Kenya, Uganda, the United Republic of Tanzania, Zambia, Malawi, Zaire, Ethiopia and Vietnam with the intention of permanently settling in India.

Required qualification:
The applicant should hold a degree of any of Universities incorporated by an Act of the Central or State Legislature in India