Detectives are questioning a 59-year-old man over online threats against Tory MP Louise Mensch.
The suspect is in custody after being arrested in Gloucester on Thursday accused of malicious communication via email and a social networking site, Scotland Yard said.
Mrs Mensch claimed earlier this week that "morons" had threatened her children by email.
The Metropolitan Police's central e-crime unit and officers from the Palace of Westminster were involved in the arrest.
The spokesman said: "The 59-year-old was arrested at an address in the Gloucester area on suspicion of sending malicious communication.
"He has been taken into custody at a Gloucestershire police station, where he remains."
Mrs Mensch, who writes chick-lit novels under her maiden name Louise Bagshawe, has three children and was elected MP for Corby last year.
On Monday she posted a message on Twitter claiming that her children had been threatened by email and said she had passed the message to police in the House of Commons.
She said: "I don't bully easily, kids. Or in fact at all."