Not directly (meaning that statement like 'GRANT EXECUTE ON trigger_name TO someone' doesn't exist).
As the database triggers are associated with tables, granting privilege(s) on the tables automatically grant privileges on the trigger(s). For example:
SQL> create table brisime (id number, name varchar2(10));
SQL> create or replace trigger trg_brisime
2 before insert on brisime
3 for each row
5 select nvl(max(id), 0) + 1 into :new.id from brisime;
SQL> grant select, insert on brisime to littlefoot;
SQL> connect littlefoot/bigfoot@ora8
SQL> insert into scott.brisime (id, name) values (null, 'Littlefoot');
1 row created.
SQL> select * From scott.brisime;
As you can see, trigger was never granted itself, but the code works properly.