The Metropolitan Police said a 62-year-old man was arrested on Monday on suspicion of an offence contrary to Section 4A of the Public Order Act.
He remains in police custody.
The arrest comes after footage shared on social media showed demonstrators confronting Newsnight political editor Nicholas Watt near Richmond Terrace and Whitehall.
Mr Watt, who was wearing a BBC lanyard, was forced to run through the mob beyond a line of police officers as people shouted “Traitor” and other slurs at him 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 previously said that 57-year-old Martin Hockridge had been charged in connection with the incident.
Hockridge, of Harpenden, 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 Tuesday June 29.
The treatment of Mr Watt was widely condemned by figures including the Prime Minister and Home Secretary as “disgraceful” and “appalling”.
Mr Johnson tweeted: “Disgraceful to see the hounding of Nick Watt doing his job. The media must be able to report the facts without fear or favour – they are the lifeblood of our democracy.”
Ms Patel added that the safety of journalists is “fundamental to our democracy”.
The BBC said in a statement after the footage was shared: “This behaviour is completely unacceptable.
“All journalists should be able to carry out their work without intimidation or impediment.”
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.