After the seizure last month, Niyazova had fled to Kyrgyzstan, but then tried to return on Monday apparently because she was told the criminal investigation against her had been closed.
Uzbek authorities have refused to comment on the detention.
Niyazova is well-known among rights activists in Uzbekistan, having been affiliated with, among others, the US-based Human Rights Watch and Internews Network, a media support group.
Niyazova "was threatened with these charges for political reasons," Holly Cartner, Human Rights Watch's director for Europe and Central Asia, said.
"In our view, the authorities wanted to intimidate Umida [Niayzova] into stopping her human rights work."
The government of Islam Karimov, the president, has cracked down on independent media and foreign-funded aid groups since a mass uprising in the eastern city of Andijan was ended bloodily by security forces in May 2005.
Western governments, including the US, called for an independent investigation into the uprising and into reports that hundreds of civilians were killed.
Several rights activists in Uzbekistan have been assaulted, detained and forced to undergo psychiatric treatment or sentenced to long prison terms for what they have called trumped-up charges of embezzlement and extortion.
Foreign non-governmental organisations and aid groups have also faced criminal charges and been forced to close down.
Karimov has been the autocratic ruler of Uzbekistan since independence and has set about limiting political opposition and silencing critics of the government.