If they are on the same multisite WordPress installation, yes.
* Visit Tools > Export on the site you want to move.
* Export your data.
* Visit Tools > Import on the destination site.
* Import the data.
Hi James, thanks for you reply. I would like to merge two or more forums in the same BBpress installation (one single WordPress), not from two differents BBPress.
Is that possibile?
Currently there is no way to ‘bulk merge’ topics from one forum into another forum.
You can edit individual topics to move them to another forum though.