Toronto Public Health says an individual at the all-boys Chaminade College School contracted the infection.
Toronto Catholic District School Board officials would not specify whether the infected individual is a student or staff member but say the person is recovering at home.
Public health officials say the risk of exposure is very low and only those with prolonged contact with the individual would require a checkup.
Last month, a person at Mary Ward Catholic Secondary School in east Toronto contracted tuberculosis.
Toronto Public Health says there were 310 cases of TB reported in the city in 2011 — most of them involving people who had lived in or travelled to an area where TB is endemic.