The 62-year-old was detained on suspicion of an offence contrary to Section 4A of the Public Order Act, according to the Metropolitan Police.
It is the second arrest made following footage shared on social media showed demonstrators confronting Newsnight political editor Nicholas Watt near Richmond Terrace and Whitehall in the capital.
Mr Watt, who was wearing a BBC lanyard, was forced to run through the mob beyond a line of police officers to get away from a group of protesters on Monday last week.
Crowds had gathered in Westminster to protest against the government’s extension of coronavirus restrictions in England by four weeks.
The Met said late on Monday evening a 62-year-old had been arrested earlier in the day and remained in custody at a police station in south London.
The force previously said another man, Martin Hockridge, had been charged in connection with the same incident.
Mr Hockridge, a 57-year-old from Harpenden in Hertfordshire, is accused of using threatening, abusive or insulting words or behaviour towards another person with the intention to cause them harassment, alarm or distress.
He was also charged under Section 4A of the Public Order Act and is due to appear at Westminster Magistrates’ Court on 29 June.
The treatment of Mr Watt by protesters was condemned by ministers after footage of the incident was widely shared on social media, with Boris Johnson calling it “disgraceful”.
The BBC also spoke out against the behaviour caught on camera, which the broadcaster called “completely unacceptable”.
The Met say enquiries into the circumstances are ongoing, and anyone with information should call 101 or tweet MetCC.
Information can also be provided to Crimestoppers anonymously by calling 0800 555 111.
Additional reporting by Press Association