Extinction Rebellion is expected to block a main road and one of the bridges across the River Ouse from 11am, after blockading five London routes as part of a “rebellion day” on Wednesday.
Police say they hope to keep any disruption to a minimum.
A spokesperson for the force said: "Residents, businesses, visitors and transport providers are advised that the activity may cause some traffic disruption in central York.
"North Yorkshire Police will continue to work alongside the City of York Council and other community partners to ensure any disruption is minimised.
"To keep up to date with the police operation, people are advised to visit the North Yorkshire Police website and social media accounts - facebook.com/NorthYorkshirePolice and @NYorkPolice."