Oracle Enterprise Manager Database Console - default login and password?
Here is the Oracle 11.2 installation document describing the administrator user accounts after installation.  Once logged in, you would change passwords with the syntax

alter user system identified by mynewpassword;


Note the SYS and SYSTEM accounts are assigned the DBA role. The DBA role does not have a password, the accounts do. The DBA role is created with every installation. You could grant the DBA role to another user if needed.