INSERT INTO R01 (NUMERO,EXPORTADOR, IMPORTADOR, DATAANTECIPADO, STATUS)
VALUES
(64, 'CCB TESTE LTDA.', 'CCB TESTE LTDA.', (select     cast('Now' as date) from rdb$database), 'A')
WHERE NOT EXISTS ( SELECT * FROM R01 WHERE NUMERO=64 ,SERIE='CTE' );

CREATE OR ALTER PROCEDURE SP_STACKOVERFLOW (
    p_numero integer,
    p_serie varchar(3),
    p_exportador varchar(255),
    p_importador varchar(255))
as
declare variable existe integer;
declare variable dataatual integer;
begin

  select
     count(r01.<id da sua tabela>)
  from
    R01
  where
    numero = :P_NUMERO and
    serie = :p_serie
  into
    :existe;

  if (existe = 0) then
  begin

    dataatual = current_date;

    INSERT INTO R01 (NUMERO, EXPORTADOR, IMPORTADOR, DATAANTECIPADO, STATUS)
    VALUES
        (:p_numero, :p_exportador, :p_importador, :dataatual, 'A');
  end

end

execute procedure SP_STACKOVERFLOW(64, 'CTE', 'CCB TESTE LTDA.', 'CCB TESTE LTDA.');

INSERT INTO R01 (NUMERO,EXPORTADOR, IMPORTADOR, DATAANTECIPADO, STATUS)
    select 64, 'CCB TESTE LTDA.', 'CCB TESTE LTDA.',
    (select cast('Now' as date) from rdb$database), 'A')
    from dummy
    WHERE NOT EXISTS ( SELECT 1 FROM R01 WHERE NUMERO=64 ,SERIE='CTE' );