If its a EX, all you would need is a factory remote(no, they are not all the same) and get it programed to the car.
If its a LX, the car did not come with any keyless unless it was added
by the dealer as a stand alone keyless, or a Honda alarm which included
the keyless. Ether way, both were expensive to buy and have it installed.
(Not $50 like last poster stated, that was just for 98-00 Civics)
The cheapest way to go is to have a aftermarket alarm installed, unless
you feel a need to have a factory unit.