  Compressional Alfv\'en eigenmodes (CAE) driven by energetic ions have been
observed in magnetic fusion experiments. In this paper, we show that the modes
can also be driven by runaway electrons formed in post-disruption plasma, which
may explain kinetic instabilities observed in DIII-D disruption experiments
with massive gas injection. The mode-structure is calculated, as are the
frequencies which are in agreement with experimental observations. Using a
runaway electron distribution function obtained from a kinetic simulation, the
mode growth rates are calculated and found to exceed the collisional damping
rate when the runaway electron density exceeds a threshold value. The
excitation of CAE poses a new possible approach to mitigate seed runaway
electrons during the current quench and surpassing the avalanche.
