  We set up and study the hydrodynamic theory for active fluid and tethered
membranes. We focus on those membranes which are inversion-symmetric. We show
that such membranes are either described by appropriate linear hydrodynamic
equations, which are exact in the asymptotic long wavelength limit, giving
stable flat phases with positional quasi long range orders, or be linearly
unstable, implying crumpling of the membranes. We argue that in a such an
active membrane thermal noises dominate over any active noises, and use it to
calculate the correlation functions of the undulation and in-plane
displacements of the membrane in the stable case, and the associated
correlation functions of the embedding bulk flow velocities.
