Byte-code representations in active networks provide architectural neutrality and code compactness; however, the resulting execution speed is typically poor due to interpretation overhead. This paper shows that the performance of capsule-based active networks can benefit from compiling active network programs into native network processor instructions at traversed routers (just-in-time compilation). A key aspect of the paper is to demonstrate that just-in-time compilers for active networks can be fast and small enough for applicability in the datapath of network processors. The approach has been implemented based on the SNAP active network framework for the PowerNP network processor.