The official Nghe An newspaper said Nguyen Nang Tinh was found guilty of publishing photos, videos and comments on his personal Facebook page with messages to instigate demonstrations and oppose the government.
It said Tinh, as a musical teacher, also taught his students anti-state songs.
The New York-based group Human Rights Watch said the half-day trial ended with a predetermined sentence.
“This long prison sentence, and the show trial that produced it, demonstrate precisely why Vietnam’s courts are the biggest jokes in ASEAN when it comes to justice for the accused,” Phil Robertson, the group’s deputy Asian director, said in a statement.
Vietnam, a member of the 10-country Association of Southeast Asian Nations, does not tolerate dissent or criticism of its ruling Communist Party.
On Friday, the authorities arrested a human rights activist at Hanoi’s airport as she returned home after four years, Human Rights Watch said.
Earlier in the week, a court in Ho Chi Minh City sentenced three Viet Tan members, including one Australian, to 10 to 12 years in jail.
Viet Tan says it is working for social justice and democratic change through peaceful means.