AC coupling of a transistor
Generally when you said 'biased at', that is the DC operating point. By analyzing the DC voltages with no input, several key parameters are measured/calculated. Some of these are transconductance, gain, I_C, and input/output impedance. 

Adding a cap to a DC-biased circuit will not affect the operating point once it charges to the node voltages. There is no DC current through the cap, so at DC the cap is perceived as an open.