Dorrit Borgaard of the public prosecutor's office said the arrest of Moroccan-born Said Mansour was based on a tip from London's Scotland Yard, The Copenhagen Post reported Tuesday.
"We received information from the British police, which led to raids at several addresses in Copenhagen," Borgaard said.
The raids in Denmark followed a series of raids in London that included the home of radical cleric Abu Qatada, the BBC reported.
Scotland Yard is investigating whether the preacher published extremist material online while on bail and fighting deportation from Britain.
Mansour became a Danish citizen in 1988 after moving to the country in 1983.
He spent 3 1/2 years in prison after being convicted of promoting terrorism in 2007.