Anti-terrorism police detained Ariana Rahma, one of the wives of Malaysian fugitive Noordin Mohammad Top, TVOne and MetroTV said without citing sources.
Police officials contacted by telephone could not confirm the reports.
This photo released by the Indonesian National Police in Jakarta, Indonesia, on Wednesday, July 22, 2009, shows police sketches of two men believed to have carried out the suicide bombing attacks on the Ritz-Carlton and J.W. Marriott hotels last week. (Photo: AP/Indonesian National Police)
However, investigators who spoke on condition of anonymity because they were not authorized to talk to the media said Rahma was among four people detained in the town of Cilacap in central Java.
They said Rahma was being taken to Jakarta, where suicide bombers at the J.W. Marriott and Ritz-Carlton hotels killed seven people, including six foreigners, and wounded more than 50 on Friday. It was the first major terrorist attack in Indonesia in nearly four years.
Eleven people remained hospitalized Wednesday.
No suspects have been officially named, but terrorism experts and investigators were quick to blame the Southeast Asian terrorist group Jemaah Islamiyah or its violent offshoots, which carried out a string of al-Qaida-supported attacks between 2002 and 2005.
Noordin joined Jemaah Islamiyah in 1998 after brief training in the southern Philippines.
Counterterrorism police have stepped up the manhunt for Noordin, who has been at large for many years and narrowly escaped capture several times, saying explosives found at the scene Friday were "identical" to those used in earlier blasts.
On Wednesday, Indonesian police issued sketches of the two men believed to have carried out the suicide attacks, while Malaysian police questioned three of Noordin's supporters.
Noordin allegedly planned the 2002 and 2005 Bali bombings and attacks on the J.W. Marriott and Australian Embassy in 2003 and 2004. Together they killed more than 240 people.
The latest bombings killed three Australians, a Dutch couple, a New Zealander and an Indonesian cook. One of the Australian victims was the first diplomat from the country to die in a terrorist attack.