yes 90% of the time it will be the passenger seat sensor.
It could be just the wires (sometimes red, or yellow on different models) that have come loose. Feel under the front of the seats for them and make sure their connections are secure.
failing that, ensure that the wires going into the buckle itself are secure (mine broke here).
if that fails then its most likely the seat base sensor mat, which requires to to remove the seat cloth/leather to slide the sensor mat out and fit a new one.
hope this helps
derek