The seven were arrested in South West Garo Hills district in an operation last night, IGP (operations) GHP Raju said.
"The group was interrogated and we came to know that the GNLA was planning to carry out explosions in West Garo Hills district before Christmas.
"One of the targets was Ampati market in the district," said Raju.
The plan was to kill both civilians and security forces, he said, adding other teams of the GNLA were also dispatched to different Garo Hills region to carry out blasts.
An IED blast at Rewak area in South Garo Hills district killed two policemen and injured three others three days ago.
Chief Minister Mukul Sangma yesterday said measures to neutralise militants would remain the top agenda of his government.