It depends on where it is. In the United States, the FBI is responsible for the anti-terrorism intelligence activities in the United States and the handling of all major criminal cases in the United States. Similar to China's National Security Agency+Ministry of Public Security, the CIA has no domestic action power.
The CIA is responsible for intelligence activities and covert operations outside the United States. In foreign countries, the CIA is better, and the activities of the FBI abroad are limited to discussing extradition with the host government.