Police said the man, who is accused of giving details of air force exercises to Pakistan’s powerful Inter-Services Intelligence (ISI), had fallen victim to a “honey trap”.
“Ranjith KK has accepted to have passed Air Force-related information pertaining to a recent Air Force exercise, movements of aircraft and deployment of various units in Air Force,” said Ravindra Yadav, Delhi police joint commissioner of crime, in a statement.
The arrest comes days after Indian Prime Minister Narendra Modi paid a surprise visit to his Pakistani counterpart Nawaz Sharif to try to ease troubled relations.
The nuclear-armed rivals frequently accuse each other of spying on military activities.
The two have fought three wars since gaining independence from Britain in 1947 and a lasting peace deal has so far proved elusive, with deadly violence still flaring in the disputed territory of Kashmir.
Police claimed that the ISI used a woman to lure him into passing on top-secret information through mobile phone and the Internet.
“As per the investigation so far, it has been assessed that (he) was befooled by the cross-border spies,” Yadav added.