According to the latest issue of Jump, the next Final Fantasy game will be coming to the Nintendo 3DS, titled Final Fantasy Explorers. It is a title that will have you battling monsters while going on a quest to gather crystals, much like the older classic Final Fantasy titles.
It was also mentioned that Final Fantasy Explorers will support up to four players, though it is unclear whether this will be co-operative gameplay or some sort of versus mode. The scan shown in Jump magazine features a white mage, black mage, a monk or a fighter, and a knight, all four of which are classic character types from older Final Fantasy games.
This announcement of Final Fantasy Explorers is currently only for Japan, and no word on a western release has been given just yet.