According to Superintendent of Police Arun Kumar Singh, the paramilitary personnel unearthed the landmines, each weighing 20 kg, after getting a tip-off that the CPI-Maoist had planted them to blow up the school as security forces used it as camp while on long-range patrolling.
The Maoists have a track record of blowing up structures used by security forces during anti-insurgency operations, officials said.
In the early hours of October 31, Maoists had razed a vacant building near the Madhuban police outpost in Giridih.
CRPF and BSF personnel were camped close to the building. Two landmines were also found in an adjacent building.