Ms

Hi Sumitra,

Yes, you can use the rail pass for the Narita express. Though you need to reserve a seat for this train (there are no unreserved seats in the N'ex).
You can make the seat reservation at the exchange office at Narita airport. The staff there speaks English.
If it is not too busy, you can also ask them to make other trainreservations in advance (if you want to reserve seats for other JR trains, like shinkansen).
If its busy though, they will exchange the voucher for the railpass and make the reservation for the train to Tokyo only.