An off-duty NYPD traffic agent was robbed at knifepoint on a Brooklyn train Thursday morning, cops said. 

The 38-year-old man was riding a northbound L train at the Sutter Avenue station in Brownsville around 11:15 a.m. when five suspects approached him — one with a knife, cops said. 

The crooks made off with the agent’s iPhone and wallet, police said. 

No injuries were reported. 

The suspects fled, and no arrests had been made by the afternoon.