Is it possible to convert .arf recordings directly to .mp3 format?
Converting WebEx Advanced Recordings directly to MP3 Audio Files (.arf to .mp3 conversion) is, per se, not possible; at least not without a workaround.
WebEx software typically allows users to export its ARF recordings in various video formats, such as for instance MP4. You can then easily convert MP4 to MP3.
Utilities for WebEx conferencing