The superstar, formerly of boy band One Direction, is shooting scenes for the film – My Policeman – in Brunswick Square.
Filming for what is believed to be a wedding scene is taking place at Regency Town House, which is usually a museum.
Ronnette Lucraft, owner of the nearby Brunswick Square Hotel, snapped images of film crew vans lining the street – as well as a shot of Mr Styles wearing a mask.
She said: “We’re not able to open because of Covid so it’s quite exciting something is going on in the square.”
It comes just days after Mr Styles was seen filming at The Vine pub in Tarring High Street, Worthing – see more here.
The 27-year-old was captured kissing his co-star Emma Corrin outside the pub as crew members and security guards stood nearby.
Large numbers of film set trailers were also seen at Worthing Leisure Centre and the popstar was also spotted in Steyne Gardens.