Yes, but only as a single bonded pair. Clownfish are sequential hermaphrodites - the dominant fish becomes female, the subordinate stays male. Two clownfish in a tank pair off naturally. Adding a third clownfish is high-risk; the established pair will usually attack and kill the newcomer. Buy two captive-bred juveniles of the same species at the same time and let them sort it out.
Clownfish biology is unusual. Every clownfish starts life as a male. The dominant fish in a group transitions to female, and the size hierarchy is enforced through aggression. Add a third fish to an established pair and the female will typically harass the newcomer until it dies of stress or jumps out of the tank.
Buy two captive-bred juveniles of the same species - both Ocellaris, both Percula, both Onyx, both Snowflake, etc. Different species do not pair up reliably. Add both at the same time, ideally in a quarantine tank first, then move them together to the display. The larger or more dominant fish becomes female within 1-3 months; the smaller stays male and a stable pair forms.
Ocellaris and Percula will sometimes pair, but designer clownfish like Wyoming White, Davinci, and Black Ice are all Ocellaris cultivars and pair fine with each other. Maroon clownfish (Premnas biaculeatus) are aggressive enough that they should never be paired with any other clownfish - they will kill anything else in the genus.
Risky. The existing fish has imprinted as either female or as a dominant male and will defend its territory. The safest move is to remove the existing fish, add both fish to a separate tank together, and reintroduce the pair to the display once they are bonded.