Boko Haram is trying to expand its activities beyond Nigeria's mainly Muslim north, to include the commercial capital Lagos, as well as other parts of the country, officials say.
Nigeria's intelligence agency says 12 members of the Islamist militant group have been arrested in Lagos since July.
It is not possible to independently verify details of the statement.
Boko Haram has waged a six-year insurgency in Nigeria, mainly in the north-east of the country.
Authorities arrested other self-confessed Boko Haram members in the south-eastern city of Enugu as well as other parts of central and northern Nigeria, the Department of State Services (DSS) said in a statement.
The DSS attributes the attempted expansion of Boko Haram into southern areas to the increased pressure the group is under in its north-eastern heartland.
However, the BBC's Will Ross in Lagos says the group is still causing havoc in the north-east, with reports that more than 50 people were killed in an attack in Borno State on Friday, about 100km (62 miles) north of the state capital Maiduguri.