It was not immediately clear what charges would be filed against Shannon Guess Richardson of New Boston, Texas, a mother of five who has played bit roles in television shows.
Davilyn Walston, spokeswoman for the U.S. attorney's office in the eastern district of Texas, said Richardson was arrested around noon Friday. She declined further comment, saying she wasn't in position to provide further details.
FBI agents wearing hazardous material suits were seen going in and out of her house Wednesday in New Boston, about 150 miles northeast of Dallas near the Oklahoma and Arkansas borders. Officials have said the search was initiated after Richardson contacted the FBI and implicated her husband, Nathaniel Richardson.
An attorney for Shannon Richardson, 36, couldn't immediately be found.
John Delk, who represents Nathaniel Richardson, told the AP on Thursday that his client had filed for divorce and may have been set up by his wife. He said his client was cooperating with authorities investigating the letters, which were sent last month to Bloomberg, his Washington gun-control group and the White House threatening violence against gun-control advocates.
"There are a lot of factors I'm aware of that indicate (Nathaniel Richardson) was set up in this deal by her," Delk said.
Delk said his client, a 33-year-old Army veteran, came to him to discuss a potential divorce a year ago and finally hired him on May 6, weeks before the ricin incident came to light.
Shannon Richardson's resume on the Internet movie database IMDb said she has had small television roles in "The Vampire Diaries" and "The Walking Dead." She had a minor role in the movie "The Blind Side" and appeared in an Avis commercial, according to the resume.
Delk said the Richardsons were expecting their first child in October. Shannon Richardson also has five children ranging in age from 4 to 19 from other relationships, four of whom have been living with the couple in the New Boston home, the attorney said.
The FBI is investigating at least three cases over the past two months in which ricin was mailed to Obama and other public figures. Ricin has been sent to officials sporadically over the years, but experts say that there seems to be a recent uptick and that copycat attacks — made possible by the relative ease of extracting the poison — may be the reason.
If inhaled, ricin can cause respiratory failure, among other symptoms. If swallowed, it can shut down the liver and other organs, resulting in death. The amount of ricin that can fit on the head of a pin is said to be enough to kill an adult if properly prepared. No antidote is available, though researchers are trying to develop one.