I am a U.S. Citizen resident in Costa Rica. Do I need to file taxes in Costa Rica ?

Maybe.  Costa Rica taxes income earned in Costa Rica.  If you are a US citizen and you have earned income from Costa Rican sources you will have to register with the Costa Rica tax department and file a local income tax return.  If you DO NOT receive any income from Costa Rican sources then you do not have to file a Costa Rica tax return.