Activists belonging to Demosisto and the League of Social Democrats (LSD) held a protest outside the police headquarters, accusing them of bias and political suppression.
They said the arrest of seven people on Wednesday morning over an anti-Beijing protests held in November were proof of this.
The protesters alleged that police is being unfair as they have yet to book anyone for the assault on Demosisto lawmaker Nathan Law on Sunday at the airport
LSD chairman, Avery Ng, said this is not the first time that they have experienced such political suppression and biased treatment.
He said pro-government protesters usually can do "whatever they want" whereas pro-democracy protesters usually face a lot more action.
LSD’s Dickson Chan, who is one of the seven arrested, said police are more active when it comes to action against anti-government protesters.
The protesters also handed over a petition asking the police to take action against those who assaulted Law.