In this work, we developed ZnFe2O4/PANI/rGO nanocomposites based on coconut shell waste through in situ polymerization as excellent radar-absorbing material (RAM). This research mainly focused on adjusting the ZnFe2O4 content to obtain optimal absorption of radar waves, especially in the X-band. The results showed that the diffraction pattern of the ZnFe2O4/PANI/rGO nanocomposites showed multiple phases (crystalline and amorphous), which increased the ZnFe2O4 content and affected the increasing diffraction intensity. The functional group of the ZnFe2O4/PANI/rGO nanocomposites was identified with the presence of the M–O group originating from ZnFe2O4 at wavenumbers 517 and 419 cm−1 of Zn–O and Fe–O groups, respectively. Meanwhile, quinoid and benzenoid rings from PANI and CO from rGO were identified at wavenumbers 1580, 1504, and 1710 cm−1, respectively. The morphology of the ZnFe2O4/PANI/rGO nanocomposites showed PANI was distributed on the ZnFe2O4 nanoparticles, which were subsequently deposited on the rGO. The ZnFe2O4/PANI/rGO nanocomposites exhibited superparamagnetic properties, as confirmed by their coercivity values ranging from 9.2 to 124.4 Oe. Interestingly, the ZnFe2O4/PANI/rGO nanocomposites with the P3 sample showed optimal RAM performance with a minimum reflection loss value of −39.8 dB at 7.6-GHz frequency with an effective absorption bandwidth of 1.1 GHz.