A 32-year-old man, whose name is not being released, was arrested Wednesday in Bristol on suspicion of committing an offense under the Protection of Harassment Act, police said.
The man's alleged threats were sent to parliamentarian Stella Creasy and campaigner Caroline Criado-Perez, The Guardian reported.
The messages were sent after Criado-Perez's successful campaign to improve the representation of women on banknotes.
After the Bank of England announced that Jane Austen would appear on banknotes in 2017, Criado-Perez and her supporters, including Creasy, received offensive messages on Twitter threatening them with rape and murder.
Twitter said it plans to make reporting abuse easier by bringing a "report abuse" button that is already available on the iPhone app version to other phone apps and the web version.