The court in southern Dong Nai province found Pham Minh Vu, Do Nam Trung and Le Thi Phuong Anh guilty of "abusing democratic freedoms to infringe on the interests of the state," lawyer Tran Thu Nam told AFP.
Vu, the only defendant to deny the charges, was given 18 months in jail while Trung was handed 14 months in jail, and Anh received 12 months, Nam said after the end of the half-day trial.
The three were arrested in May last year and originally accused of disrupting local traffic in Dong Nai, but the charges were later changed.
The three were subsequently charged under Article 258, one of the provisions of the penal code which rights groups say is deliberately vague and used to prosecute regime critics.
Also Read
Scores of bloggers and vocal regime critics have been charged under Article 258.
Vietnam's Communist Party, which has run the unified country since 1975, is sensitive to any public criticism of its rule.
Early this week, authorities allowed well-known writer Nguyen Quang Lap and blogger Hong Le Tho, both of whom had been arrested on similar anti-state charges, to be released on bail ahead of the lunar new year holiday, which starts next week.
A number of other high-profile bloggers remain in custody, awaiting trial.
According to Reporters Without Borders, Vietnam is currently holding at least 34 bloggers in prison.