From the Asus website (http://www.asus.com/product.aspx?P_ID=2UYSq8dAHOj0k84O),
in the specifications tab, the board shows that it has 1 COM (a.k.a. serial port) port. However, from looking at what is included with the motherboard, I don't see a serial port adapter cable that would plug into the motherboard and then to a bracket. This is definitely not a serial port in the I/O panel.
BTW, what do you need to connect via serial port? They are not used very much these days.