The couple have been dating since November 2009. Lampard had split from partner Elen Rivas, with whom he has two daughters, a year earlier.
A spokesperson said: "I am pleased to say that Christine Bleakley has accepted Frank Lampard's surprise engagement proposal here in Los Angeles.
"They are obviously both delighted but there are no immediate wedding plans, and the couple will not be making any further comment on this happy and private occasion."
Lampard had reportedly planned to pop the question to Bleakley while they were abroad so that they would be engaged on their return to London this month.
A source claimed that he planned to "propose in the most romantic way possible".