Informal:
* Je viens d'arriver. (Literally: "I come from arriving.") This is the most common and natural way to say it.
* Je suis arrivé(e) il y a peu. (Literally: "I arrived a little while ago.")
* Je suis rentré(e) tout à l'heure. (Literally: "I came back a little while ago.") This is more specific to returning home.
Formal:
* Je suis de retour. (Literally: "I am back.") This is a more formal way to say it.
You can also use the past participle of the verb "to return" (revenir) with the auxiliary verb "être" to indicate that you have just returned. For example:
* Je suis revenu(e). (Literally: "I am returned.")
The best way to say "just got back" in French will depend on the specific situation and the level of formality you want to use.