A 21-year-old man was arrested at Birmingham Airport and two women and two men aged between 22 and 47 were held at Manchester Airport.
A 30-year-old man was arrested in the Rochdale area earlier this month.
Greater Manchester Police said they were arrested on suspicion “of CPI Section 40 (1) (b) Tact 2000 (Commission, Preparation or Instigation of acts of Terrorism)”.
The force said today that all six have now been released without charge.
An investigation was launched by the North West Counter Terrorism Unit after nine people were stopped by Turkish authorities at the Turkey/Syria border.
A GMP statement said: “No evidence was uncovered to suggest any imminent threat to the communities of Rochdale or the UK.”