Police spokeswoman Els Cleemput said at least 90 officers were used to remove the 56 protesters from the aircraft, which was moved away from the terminal at Brussels airport after negotiations failed to end the protest action at 0230 GMT.
"The plane is now empty," Cleemput said on Friday, adding no handcuffs had to be used and there were "no major incidents".
She said, however, some protesters had to be carried out, refusing to leave on their own.
Cleemput said all those detained were bused to a detention centre at the airport where their identities were to be checked. She said most were unlikely to be charged.
It was unclear if or when the protesters would be repatriated to their country of nationality.
Cleemput said police and Belgian foreign ministry officials decided to cut off negotiations after protesters refused their offers to leave the plane without fear of arrest after hours of negotiations that stretched into the night.
"We tried to find a compromise. Unfortunately this did not work," Cleemput said. "We wanted to ensure that flights could operate safely in and out of the airport on Friday."
She said three of the 59 protesters had decided to leave the plane prior to the police action, which took around an hour, starting after 0330 GMT.
The group of unarmed Iranian pro-monarchist protesters was demanding the European Union, the United States and Russia not cooperate with the Iranian government, which the group wanted overthrown.
A spokesman for the group on the plane demanded the EU, the US and other nations sign a declaration denouncing the Iranian government.
Supporters of the protesters
held banners at the airport
"We won't be moved from here unless we die and they take our bodies from the airplane," said a man who gave only his first name, Ira, in a telephone interview earlier on Thursday from the plane, adding the group had started a hunger strike.
Police denied the group's members were on a hunger strike, saying several passengers took food and drink during the night.
Ira said the group included four children and 22 women.
He said his group, which he called Anjoman-E Padeshahi Iran, or the Assembly for a Monarchy for Iran, "were not terrorists" but "messengers of peace".
Police said 59 passengers refused to the leave the plane, out of the total 103 that took the flight from Frankfurt, Germany.
The stand-off began shortly after the flight landed at 3pm (1400 GMT) on Thursday.
Ramin Atashagar, a spokesman for the group at the airport, said the Belgian authorities had betrayed the protesters by cutting off negotiations.
"They wanted to betray the Iranians who were in the airplane," said Atashagar.
About 40 people were at the airport supporting the group's protest, waving flags and holding banners.