The actress announced the happy news on her Tumblr blog on Tuesday night (24Feb15), posting photos of her and her husband as children, along with a graphic of a "bun in the oven."
She added the caption, "Surprise! We're having a baby! Ryan and I feel so blessed and can't wait to welcome the newest member of our family."
The baby news comes days after Rivera wrapped filming on the Golden Globe-winning programme on Saturday (21Feb15). Glee ends its six-season run in the U.S. next month (Mar15).
Rivera and Dorsey secretly wed in Mexico last July (14), just three months after the actress ended her engagement to rapper Big Sean.