James Scott, now editor of The People, Tina Weaver, a former editor of the Sunday Mirror, and two others were picked up at their homes at about 6 a.m., The Guardian reported.
Sources told the Guardian the four are suspected of being involved in intercepting cellphone voice mails about a decade ago at the Mirror.
"This conspiracy is being treated as a separate conspiracy to the two being investigated at the now defunct News of the World newspaper," the Metropolitan Police said in a statement.
Scott is the first sitting editor to be arrested in the investigation known as Operation Weeting.
The phone-hacking scandal began with allegations media mogul Rupert Murdoch's News of the World hacked into the voice mails of celebrities and members of the royal family. It exploded after the Guardian reported in 2011 News of the World had allegedly hacked the cellphone of Milly Dowler, a missing schoolgirl who was found dead months after she vanished in 2002.
Murdoch closed the Sunday tabloid in 2011.