Mysterious Voltage Bias
1000 &micro;F is a ridiculously huge value to use as the coupling capacitor at the output of the amplifier, especially given the high input impedance of the filter(s). Assuming this is an electrolytic capacitor, its leakage current is undoubtedly enough to explain the bias you're getting.

Assuming that the net input impedance of your three filters together is on the order of 100 k&Omega;, a ceramic capacitor of 0.1 &micro;F for C2 would give you a lower cutoff frequency of 16 Hz, which is plenty low enough for this application.