One of the men was detained while trying to take a flight from London's Gatwick airport on Wednesday, while the others were arrested at addresses in east London on Thursday, it said in a statement.
The man arrested at the airport is aged 33 while the others were aged 18, 22 and 31, police said, adding that they were being held by the Metropolitan Police's Counter Terrorism Command.
"These arrests form part of an investigation into travel to Syria in support of alleged terrorist activity. Inquiries continue," police said.
"Two men have previously been charged in connection with this investigation."
A British trainee doctor, Shajul Islam, 26, and another man, Jubayer Chowdhury, 24, are due to go on trial in Britain in June charged with the kidnapping of two Western journalists by Islamic extremists in Syria.