Governor K Rosaiah administered him the oath of office and secrecy at the Raj Bhavan here in the presence of the Chief Minister.
Mohan will handle the Rural Industries portfolio, which includes Cottage and Small Industries.
A first-time Minister, Mohan, elected from the Sankarapuram Assembly constituency, was recently inducted in a minor reshuffle by Jayalalithaa who dropped C Ve Shanmugam from the ministry.