(CNN) -- Myanmar authorities have released an American human rights activist who was handed a five-year prison sentence in February.
Zaw Lwin, 40, was freed Thursday, government officials said. It was not immediately clear why he was released early.
The activist, also known as Nyi Nyi Aung, was arrested in September 2009 at the airport in Yangon.
He was convicted of using a fake national identity card, breaching the registration act and carrying foreign currency of more than $2,000 without permission, said lawyer Nyan Win.
Because the sentences for some of the charges were to run concurrently, Zaw Lwin would have served three years in prison had he remained incarcerated.
He is a U.S. citizen who was born in Myanmar, also known as Burma, his lawyer said.
He was working for the Free Burmese Political Prisoners Now campaign in Thailand before his arrest.
His mother and two cousins are serving lengthy prison terms in Myanmar for participating in demonstrations in 2007, the lawyer said.