
Porntip Paksanon, 53, chairwoman of the Phetchaburi Red Shirts Group, arrived at Dusit Police Station at 10am for questioning.
Police charged her with threatening Somjit Nawakruasunthorn, the Channel 7 reporter, with the email.
Porntip said she had no intention of scaring Somjit, held no prejudice against the press and had not addressed the email to the reporter.
The message was forwarded by someone else, she said.
Porntip reportedly sent the email to her red-shirt friends, saying the reporter should be "taken care of at first encounter" for having posed aggressive questions to Prime Minister Yingluck Shinawatra, who reportedly had to walk away after being cornered.
Porntip said she was ready to defend herself and hoped police would handle the case straightforwardly.
Lt Col Pittinun Utthasing, deputy superintendent of Dusit Police Station, said it was a petty crime with a maximum jail term of one month and/or fine of Bt1,000, and did not come under the Computer Crime Act.
Porntip was allowed to return home after she was interrogated, he said. No arrest was made.
About 50 red-shirt followers had gathered at the station to support their leader.