She was held for eight hours and copies of her new album were confiscated, her husband told the BBC.
An outspoken campaigner for free speech, she met former US President Barack Obama during his 2016 visit.
Mai Khoi’s detention comes amid a crackdown on activists. The one-party state is often criticised by rights groups for its intolerance of dissent.
“Immigration officers questioned her about her movements and activities while in Europe and confiscated copies of her newly released album, Dissent,” Mai Khoi’s Australian husband, Ben Swanton, told the BBC.
News of her detention emerged when Mr Swanton posted on her Facebook page that she had texted him to say she was being held at the airport, despite denials by security officials there.
She posted an update later to say she had been released.
On her website Mai Khoi, 34, describes herself as “a fiercely independent Vietnamese artist”. Her new band is called The Dissidents and she has been compared by some to Lady Gaga or Pussy Riot because of her provocative style.
Her song “Please, sir” pleads with the Communist Party leader to allow everyday freedoms for ordinary people.
She was one of a small number of activists who tried but failed in 2016 to gain seats to Vietnam’s parliament, which is dominated by the ruling Communist Party.
Last November she protested against current US President Donald Trump’s visit to Vietnam.
She has not been subjected to a travel ban but is on a watchlist of dozens of dissidents for criticising the one-party system.
Human Rights Watch (HRW) says Vietnam’s human rights situation “seriously deteriorated” last year.
At least 129 people are currently detained for protesting against or criticising the government, the group says.
The authorities have overseen great economic and social change in recent years but there is strict state media censorship and pro-democracy activists are regularly jailed, beaten and threatened.
Ms Khoi came under pressure last November at the time of the Trump visit.
“They have called my parents in for questioning, raided two of my concerts, asked my landlord to kick me out of my house, refused my permit to live in Hanoi, and put me under constant surveillance,” the Washington Post quoted her as saying.
It’s not clear why she was targeted now.
HRW’s deputy Asia director, Phil Robertson, told the Guardian “she is someone who is high-profile enough that they would basically leave her alone“.
“The authorities are getting bolder,” he said. “I think the Vietnam government feels that the US and other countries are busy somewhere else and this gives them ample running room to crack down on the dissidents the way they have wanted to in the past.” (Courtesy BBC)