Under Belgian law, authorities can detain a suspect for up to 24 hours.
After that a magistrate must decide whether there are sufficient grounds to hold them further.
Guy Verhofstadt, Belgium's prime minister, said on Friday there were indications of a possible attack in preparation after police thwarted what they said was an attempt to free Nizar Trabelsi, suspected of ties to al-Qaeda, from jail.
Trabelsi, a Tunisian, was arrested in September 2001 for plotting attacks on US targets in Belgium.
He was jailed in 2004 for 10 years.
Police picked up the 14 suspects in a series of Friday morning raids.
Earlier reports indicated that explosives and arms were also seized, but Pellens said Saturday that searches of the suspects' homes had found no explosives, weapons or other evidence to persuade the court to charge them with any offense or keep them in jail.
The government's crisis centre said the investigation was continuing into other material found in the searches.
Alain Lefevre, a director of the centre, told a news conference: "The release of the 14 does not mean the investigation is finished. Depending on the results, our measures will be adapted."
The 14 were expected to remain under police surveillance and could be detained again if more evidence is uncovered.
The authorities did not release the suspects' identities.