Guests received an invitation with "Come see our new home on Android" written on it. Facebook, however, has given no additional clues as to the content of this evening's presentation, which begins at 6pm GMT.
Facebook, which has a highly successful mobile app, has previously played down its interest in producing a dedicated mobile phone, with founder and CEO Mark Zuckerberg reportedly stating in January that he was not intending to build a phone.
Rumoured features on the phone include enhanced details about a caller, including where they have recently visited on holiday. A 16gb storage capacity and a five megapixel camera are expected.
Meanwhile, check out our analysis with industry opinion on whether product launches have become too 'samey'.