A representative for Harris confirmed in an e-mail Monday that Harris made the announcement in a posting on Twitter.
The 37-year-old actor says he and Burtka are "super excited/nervous/thrilled." He did not say whether they were adopting or using a surrogate.
Harris posted the message on Saturday. He stars in the CBS sitcom "How I Met Your Mother."
CBS is a division of CBS Corp.
Online: How I Met Your Mother.