The party is headed by the Nobel Peace Prize laureate Aung San Suu Kyi.
One of the members of the NLD arrested is reported to have admitted to writing an anti-government pamphlet which was produced for public distribution.
The NLD won general elections in 1990, taking 392 of 485 contested seats, but the ruling junta has refused to recognise the victory.
Aung San Suu Kyi was released last May from 19 months of house arrest, but human rights activists say Myanmar still has 1,200 to 1,300 political prisoners despite a series of releases last year.
The Burmese authorities have been widely criticised for their poor human rights record. A delegation from Amnesty International returned from its first fact-finding mission to the country last week.
The human rights group called for the release of all political prisoners and pressed the Yangon junta to improve its rights record.
