In this paper,a chaotic-sequence-based dual-domain joint encrypted transmission scheme is proposed for affine frequency division multiplexing (AFDM) to mitigate eavesdropping threats in high-mobility 6G scenarios. First, a chaotic sequence dynamically selects the chirp parameter c2 in the parameter domain to disrupt the discrete affine Fourier transform (DAFT) matching condition at the illegitimate receiver. Then, in the symbol domain, modulation bits undergo exclusive OR (XOR) encryption with another chaotic key to conceal constellation information. Finally, the two independent chaotic sequences are combined to exponentially expand the key space, which increases the difficulty of brute-force attacks. Simulation results demonstrate that the proposed dual-domain joint encryption scheme is capable of providing substantial performance gains over single-domain encryption counterparts in terms of eavesdropper's bit error rate (BER) elevation and key space expansion, while the legitimate receiver with the correct key achieves a BER almost identical to that of the unencrypted AFDM system without incurring noticeable performance degradation.