There are rumors that Microsoft will respond to Sony's PlayStation 4 announcement by holding an event of their own, in which they'll unveil the Xbox 720, the successor to the Xbox 360.
According to CVG, a senior Sony official, who wished to remain anonymous, said that the PlayStation 4 announcement, "at first caught Microsoft off-guard," and that Sony, "definitely ruffled some feathers."
Now it is speculated that Microsoft will show off the next Xbox at an event to be held in early April. A thread on NeoGAF explains that a company called Eventcore (formerly Ustechs), has registered "XboxEvent.com" as a domain name. The company previously worked with Microsoft on events like E3 2012.
For now, nothing seems to be set in stone, but we'll update you once more information about this event is released.