In the state of North Carolina does the tenet have to turn in the keys to the property?

We were renting one side of a duplex and our landlord decided to kick us out by ending the lease. He gave us thirty days. We thought we just had to leave. However, the landlord came to my work and asked about turning in the keys. Do we have to legally turn in the keys in North Carolina? or is the landlord just trying to save money by not changing the locks?