Preston New Road was closed near Little Plumpton earlier, police said.
The force said the road was shut between Fox Lane Ends and Whitehills Business Park 'due to an incident involving protestors at the entrance to the Cuadrilla site'.
"A group had gathered and blocked the access point of the site, meaning Cuadrilla employees and vehicles couldn't leave," a spokeswoman said.
A Facebook Live video showing a large police presence close to Cuadrilla's fracking site was posted online, and showed officers standing in formation across both carriageways.
"They have shut the road at both ends," the person recording it told viewers shortly after 6pm.
The road was clear by around 6.35pm, one motorist told The Gazette, while police said at 6.40pm the road had been reopened.
Nobody was arrested in connection with this evening's closure, but three arrests were made earlier today, the police spokeswoman added.
No more information was immediately available however.