The couple, who have been together since autumn 2008, also plan to marry in a private ceremony later this year, she announced.
It will be the first child for Alicia and the third for 31-year-old Swizz, real name Kasseem Dean, who has two sons from previous relationships.
A friend of the pair revealed that they are "very happy" with the news, and it certainly showed on Thursday night, as a radiant Alicia and her fiancé attended the Keep A Child Alive Black Ball in London's Smith Square.
The Empire State of Mind singer, who co-hosted the event, looked lovely in a voluminous, feathery grey gown that hid her growing tummy.
It seems that this is her year to shine, as the happy news comes on the heels of many recent professional accomplishments for Alicia, whose music is featured in the new Sex and the City 2 movie.
The bride-to-be is currently busy touring Europe before she heads to South Africa to perform at the World Cup on June 10.