MySQL returned error

Error Description :

Error No : 1064
Description : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') GROUP BY attribute_group.id' at line 1

SQL Query
SELECT COUNT(attribute_group.id) AS CNT FROM attribute_group LEFT JOIN attribute AS attribute ON(attribute.attribute_group_id=attribute_group.id) WHERE attribute_group.id!=0 AND (category_id=) GROUP BY attribute_group.id