Rachel Goldwyn, 28, from London, became the second Briton in eight days to be detained by the Burmese authorities for demanding civil rights in the country.
James Mawdsley was detained last Tuesday and sentenced to 17 years in prison for illegally entering Burma and distributing pro-democracy leaflets.
Ms Goldwyn was arrested for chanting pro-democracy slogans and singing a song banned by the country's military regime, according to the democratic Burmese students' organisation.
The foreign office confirmed that Ms Goldwyn had been arrested and said British officials in Rangoon, the Burmese capital, had asked for details from the country's ministry of foreign affairs.
A spokesman said: "We will be asking why she has been detained, what she has been charged with and whether she has legal representation."
Witnesses to Ms Goldwyn's arrest said she was dragged into a police van after singing in front of about 300 students.
Dissidents have planned nationwide pro-democracy protests for tomorrow, 11 years after thousands of protesters were killed by the military regime during an unsuccessful uprising.
In a statement written before her arrest Ms Goldwyn said she wanted the British government to stop investing in Burma.
