SQL & PL/SQL :: Resource Busy While Creating Constraint

i am working in scott's schema and i want to create foreign key on new table that is "test" table ,structure is----

create table test(id number, name varchar2(20),dno number,pno number);

and now create a foreign key on id column of "test" table reffering the empno of "emp" table which has pk already. but it shows an error-------"ora-ORA-00054-resource busy and acquire with NOWAIT specified or timeout expired"

while i have create the "test" table just 1 min ago.