Some two dozen activists chanted "Save Tibet!" and unfurled a banner reading "Stop Genocide in Tibet" before police intervened, detaining 21 protesters outside the Panathenian Stadium. Most were later freed.
A police cordon prevented the demonstrators from disrupting the final leg of Greece's relay from the Acropolis to the marble stadium, the venue of the first modern Olympics in 1896.
"We just wanted to show our support for Tibet, peacefully, and when we displayed the flags we were taken away by police," said Klara Vrhova, a Czech member of the Students for a Free Tibet group.
Marina Staroyianni, a Greek member of the group, said protesters wanted "to let the whole world know that China is violating human rights" in Tibet.
"A lot of people are now talking about the problem, throughout the world," she added.
The flame goes Tuesday to Almaty, Kazakhstan, and then on to Istanbul, Turkey, and St. Petersburg, Russia. Those stops are not expected to bring problems, but the following three could: London, Paris and San Francisco.
London's route on April 6 is sure to be lined by thousands of demonstrators, who are expected to have a wreath-laying ceremony to commemorate those killed in Tibet's recent unrest. Tibetan exiles say almost 140 people have died, while the Beijing government puts the number at 22.
Pro-Tibet demonstrators are expected to be just as numerous in Paris on April 7. French President Nicolas Sarkozy is the first European leader to suggest a boycott of the opening ceremony as a possibility to protest China's handling of the unrest in Tibet.
In San Francisco, the only North American city hosting the torch, officials shortened the April 9 route through the city and have abbreviated the ceremonies. Mayor Gavin Newsom has said no one will be prevented from expressing his views, but permits are required to gather near the torch.
Another difficult stop comes April 17 in New Delhi. India is home to Tibet's government-in-exile and many Tibet rights groups are located in the country.
Activists want Chinese authorities to cancel plans to carry the flame through Tibet on its way to Mount Everest for the first time. China has dismissed the demand.
"The torch will for the first time ascend the summit of the world, thereby testifying to the great strength of the Olympic movement in marking the progress of human civilization," Liu said after receiving the flame.