Assistant Chief Constable Tim Mairs told a Policing Board seminar in Belfast that this week alone, five people are being brought back to Northern Ireland under the policing tool.
Making a presentation called Policing The EU Exit, Mr Mairs said police are concerned about the risk of losing this power if the UK leaves the EU without a deal.
He also outlined potential risks from a no-deal Brexit including additional infrastructure or checks at the border generating violent attacks and the exploitation of differences between the North and South.
He emphasized that police do not want to see the perception of a “safe haven” for criminals created either north or south of the border after Brexit.
The PSNI is recruiting 308 new police officers and staff to deal with Brexit after receiving additional funding of £16.4m from the Treasury.