Ministers say sweeping powers to control people`s movements are needed because the area, which borders Nigeria, is targeted by the militants.
Chad has been instrumental in helping Nigeria retake most of the areas Boko Haram had seized in northern Nigeria. But in the last few months, the group has intensified attacks in remote areas around Lake Chad.
Boko Haram is suspected of involvement in the killing of at least two people in a village in Chad on Sunday and three Nigerian refugees in northern Cameroon on Monday.
The state of emergency will give the governor of the region the authority to ban the movement of people and vehicles, search homes and recover arms, the government announced following an extraordinary cabinet meeting.
Aside from Chad, the Islamist group`s attacks have spread from north-eastern Nigeria, its traditional stronghold, to the neighbouring countries of Niger and Cameroon.
Chad is also host to a new regional force set up to tackle the Nigeria-based militant Islamists.
Benin, Cameroon, Chad, Niger and Nigeria agreed to establish the 8,700-strong force, but it has yet to start operations in earnest because of reported funding difficulties.
According to Amnesty International, at least 17,000 people, mostly civilians, have been killed since 2009, when the group launched its violent uprising to try to impose Islamist rule in northern Nigeria.
More about:
