32-year-old Abdul Wahid Siddibapa, a resident of Bhatkal in Karnataka, was held after his arrival from Dubai, NIA officials said.
Abdul is a close relative of Riyaz and Yasin Bhatkal, co-founders of IM, and was involved in providing tactical and financial support to the terror group in planning and organising its activities, they said.
"It is a big catch for the agency. His interrogation can lead to many vital inputs about the IM's activities and arrest of many other operatives," a senior NIA official said.
Abdul was wanted in a case pertaining to a conspiracy by IM to attack various places in India. He was held on the basis of a warrant of arrest and a Red Corner Notice already issued against him, the agency's official said.
He was produced before a special court today which sent him to seven days custody of NIA.