Britons Reza Pankhurst, Ian Malcolm Nisbett, and Maajid Nawaz, and 23 Egyptians, have been on trial since October last year.
They stand accused of belonging to and trying to reactivate the banned Islamic Liberation Party, and aiming to overthrow governments in the region.
The group, which emerged in Jordan in the early 1970s, seeks to restore the caliphate - one Islamic government for all Islamic states - through military coups across the region. The accused face up to 10 years in prison if found guilty.
At the first court hearing in Cairo in October 2002, Pankhurst said that he and other defendants had been subjected to prolonged torture while in custody which prompted them to make confessions they later retracted.
All the defendants have pleaded not guilty.
In July, the supreme state security court said the verdict would be pronounced in December, but the presiding judge declared on Thursday that a final decision would be taken on 25 March, without giving a reason for the delay.
"There is only one God and Muhammad is his prophet," cried some of the accused as they were led from the court after the adjournment.
"It's clear that there are political reasons for the delay," said 27-year-old British defendant Nawaz.
"It's clear that there are political reasons for the delay"
Nawaz's mother said the delay had come as "a surprise, because the British embassy told us the Egyptian authorities had confirmed" that the verdict would be handed down on Thursday.
"It's possible that the attack on the Egyptian minister (Maher) could be behind the delay," said Homira Nisbett, wife of another accused, Ian Malcolm Nisbett.
Maher was assaulted on Monday by a group of Palestinians, who called him a traitor while he visited the flashpoint Al-Aqsa mosque compound in Jerusalem.
"The delayed verdict following the attack on Ahmed Maher worries us, notably because it coincides with the arrests in the past 48 hours of 80 people accused of belonging to the Liberation Party," said defence lawyer Montasser al-Zayat.
The 80 people who were arrested had previously been detained by police, allegedly in connection with the ongoing trial, but were released because of lack of evidence, al-Zayat said.