Four people aged between 22 and 47 were arrested at Manchester airport in north west England, Greater Manchester Police said.
Police have also arrested a 31-year-old man from Rochdale yesterday.
All the six arrested remain in police custody for questioning, Police added.
The arrests have come in the wake of an investigation launched after nine people, including five adults and four children, of a family were stopped by Turksih authorities while trying to cross into Syria.
Police said they were trying to establish why the group of nine people of the same family had apparently attempted to cross the border into the war-torn country.
Waheed Ahmed, 21, held on the Turkish border as he attempted to cross into Syria was arrested at Birmingham Airport yesterday after being deported back to the UK.
Son of a local Labour politician from Rochdale, Waheed was detained along with eight family members in Hatay near the Syrian border on April 1.
