Check if Exists PLS-00405: subquery not allowed in this context

I have cursor it selects from TableA then Fetch Loop that inserts into TableB.

I want to check if the value already exists in the TableB.

If it exists then I want to skip the insert.

create or replace
PROCEDURE DAILY_RPT (
    v_start       IN DATE,
    v_end        IN DATE)

IS

    ao_out_no   out_pair.out_no%type;

cursor get is
SELECT ao_out_no from tableA;

BEGIN
 open get;
     LOOP
     fetch get into ao_out_no;
      EXIT WHEN get%NOTFOUND;
     if (ao_out_no = (select out_no from TableA where out_no = ao_out_no) THEN
     --DO NOTHING
     else 
        INSERT INTO TABLEB(OUT_NO) VALUES (ao_out_no);
     end if;

        END LOOP;
     close get;

END;

I used IF CONDITION however, I used variable into if condition & I am getting below.

PLS-00405: subquery not allowed in this context

if (ao_out_no = (select out_no from TableA where out_no = ao_out_no) THEN