As a promising technique in mitigating extremely strong and broadband jamming, active anti-jamming (AAJ) allows a transmitter node to send messages by re-modulating jamming signals with programmed amplification factors. However, how to optimize these amplification factors is still an open issue. In this letter, we propose an energy-efficient design for AAJ-enabled communications systems. In particular, the energy efficiency problem is studied and formulated as the total energy consumption minimization subject to the minimum required rate and the hardware limit of the power amplifier, which turns out to be a quadratic programming problem. The corresponding optimal amplification factors are obtained by the interior point method. Numerical results indicate that with the equal transmission rate, the proposed energy-efficient AAJ scheme can provide 76.8% energy saving as compared with the direct transmission.