Many of those convicted were imprisoned for at least seven years. Another 26, including 13 women, were acquitted.
The 94 defendants were accused of trying to seize power in the Emirates.
The verdict ended a trial criticised by human rights groups, which said the judge failed to investigate “credible” allegations of torture of defendants.
The defendants included human rights lawyers, university lecturers and students.
A majority of those convicted were given jail sentences between seven and 10 years, reports said.
Eight defendants no longer in the country were sentenced to 15 years.
The convictions were condemned by Human Rights Watch. Nick McGeehan, the organisation’s Gulf researcher, said they represented “another low point for the UAE’s worsening human rights record”.
“These verdicts cement the UAE’s reputation as a serious abuser of basic human rights,” Mr McGeehan added.
No foreign media
The Federal Supreme Court jailed two prominent human rights lawyers to 10 years in prison each, the Emirates Centre for Human Rights said.
The verdict was reported on local state-run TV.
Roads outside the court were blocked and reporters kept away from the site ahead of the verdict, Reuters news agency said.
Foreign observers and international media have not been allowed access to the hearings.
The defendants are said to be members of al-Islah, an Emirati-based Islamist group linked to the Muslim Brotherhood.
They were accused of setting up an organisation “seeking to oppose the basic principles of the UAE system of governance and to seize power”.
Political parties and demonstrations are banned in the UAE, which comprises seven sheikdoms run by ruling families.
The trial which began in March has been strongly criticised by global human rights advocates, who have said the proceedings were in “flagrant disregard of fair trial guarantees”.
Most of the defendants were arrested in July and August 2012. Their families were denied visitation rights during pre-trial detention.
Human rights groups also alleged that some of the inmates were tortured during their detention.
But the UAE attorney general has rejected the claims, saying the prisoners were being “dealt with according to the law”.
The 68 who were convicted have no right of appeal.
The UAE like other Gulf Co-operation Council (GCC) countries has cracked down hard on dissidents and social media activists.
Two more were arrested on Monday night for tweeting in support of the 94, including the brother of a prominent detainee, a local activist told the BBC. He said they were being held in an unknown location.
The activist described the detainees as “singing Islamic songs and chanting God is great” when the verdicts were announced in court.