Beijing (CNN) -- The wife of Ai Weiwei was taken from the Chinese artist's studio by police Tuesday and was questioned for three hours, the high-profile dissident said.
Four policemen took Lu Qing from the Beijing studio to a nearby police station, he said.
She was released by police after questioning and is now a "criminal suspect," he said.
They have not told her what crimes she is accused of, he added.
"I think the authorities are trying to threaten me through her," he said, speculating that Lu's arrest was related to her plans to visit Taiwan for an exhibition of her husband's work.
She has now been told to stay in Beijing, he added.
Police did not respond to a CNN request for comment on the case.
"Nobody can consider himself safe or innocent in an environment like this," said the dissident, who was himself detained by police for 81 days earlier this year.
He was ultimately charged with tax evasion, and last week paid $1.3 million so he can contest the charges brought against his company, Fake Cultural Development Ltd.
Had he not paid the sum, his wife -- who legally represents the company -- would have been jailed, he said.
The government says the company owes 15 million yuan ($2.3 million). The money was raised from 30,000 contributors, he said.
His lawyer, Pu Zhiqiang, said last week that Ai intends to return the donations if he wins the case and is refunded the money.
His family and human rights advocates believe that the real reason for his imprisonment is his criticism of the Chinese government.
Ai was released on bail in June because of his good attitude and medical concerns, according to state-run news agency Xinhua.
Local authorities held a closed hearing in July on the tax evasion allegations, despite demands for an open hearing from Ai and the company's lawyers. According to the artist, authorities also declined their demand to publish the accounting records and other evidence that lead to the tax evasion charge.
Ai said earlier this month he was initially detained and imprisoned on charges of "subversion of state power," but upon his release the charge was changed to tax evasion.