Officials said the incident was reported from the AIIMS station here when a CISF jawan noticed the man, identified as Vishal Negi, trying to hand over a book to a person from the partition that separates the general area of the station from the security hold area of the station.
The CISF jawan intercepted the man and checked the book in which a small knife was allegedly found concealed.
They said Negi told security personnel that he was trying to sneak in the knife in the book as it would not have been possible had he gone through the normal security check system.
"Negi was handed over to local police which arrested him under the Arms Act. Weapons, arms and ammunition are not allowed to be carried inside the Metro system," a senior official said.
The Delhi Metro security is already on a high alert following the subway blasts in St Petersburg in Russia on Monday that killed 14 people.