The 30-year-old actress had fuelled pregnancy rumours when she was recently spotted attending a prenatal yoga class in LA, reported People magazine.
"They are both beyond ready to be parents. They've been talking about having children for nearly a year. They are so excited for that next step," a source said.
Kunis and Kutcher, 36, who became engaged earlier this year, are apparently keen on getting hitched soon.
"I think they'll be traditional and get married before the baby is born. Ashton wants this marriage and relationship to be perfect," a source said.