Letzte Generation (Last Generation) posted video on Twitter of white T-shirted supporters scaling the wire fence before being carried away by security.
"It's time to slow down. Because we're on the highway to climate hell with our foot on the accelerator," the group said on Twitter.
A Formula E spokesperson said the protest was "unrelated to the event".
"Security services quickly and safely contained the disruption," the spokesperson added. "The event was able to proceed as planned."
City-based Formula E is the only FIA-sanctioned zero-emission all-electric world championship and takes pride in being the first sport in the world to be certified net zero carbon from the inception.
Car manufacturers Porsche, DS, Nio, Maserati, Jaguar, Nissan, McLaren and Mahindra are among the teams competing in the series.
The incident was the latest in a series targeting prominent sports events.
A Just Stop Oil protestor halted the World Snooker Championship in Sheffield last week after climbing on to a table and scattering a bag of orange powder paint over the playing surface.
Britain's Grand National horse race was delayed by animal rights protesters, with 118 people arrested.
Twenty-five people were also arrested at Saturday's Scottish Grand National.
Activists ran onto the track after an opening lap crash at last July's British Formula One Grand Prix at Silverstone.
Sunday's race started after a brief delay and was won by New Zealander Nick Cassidy (28) for Envision Racing from eighth place on the grid, with Britain's Jake Dennis (27) second for Avalanche Andretti.
DS Penske's Jean-Eric Vergne (32) finished third with Saturday's winner Mitch Evans (28) fourth for Jaguar.
Cassidy is now four points behind Porsche's championship leader Pascal Wehrlein (28), who finished seventh.
