Chatra sub-divisional police officer (SDPO) Gyan Ranjan said the six were sitting with solved Maths papers at their test centres on March 28.
"They have been detained," he said.
One of the detainees claimed they allegedly received the papers from Patna, following which a police team was sent to the Bihar capital city for further investigation, the SDPO said.
An FIR has been lodged against the four but no arrest has been made as yet, the SDPO said.
The CBSE Board examination paper leaks earlier this week has drawn widespread criticism from across the country and triggered students protest.
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