The two men and a woman aged 33 to 36 returned on a special flight that arrived at Van Don International Airport in the northern province of Quang Ninh on Monday.
All 136 passengers were immediately quarantined for 14 days in nearby Hai Phong City.
With the trio, Vietnam has had 866 cases of whom 399 have recovered and 17 have died.
Of the total number, 321 have been imported cases that were isolated on entry.
Since the novel coronavirus resurfaced in Da Nang on July 25 there have been 405 cases in 14 cities and provinces, including Hanoi and Ho Chi Minh City.
More than 134,000 people are in quarantine.
Worldwide, Covid-19 has claimed more than 744,000 lives.