It will be the first child for Hashian, a singer-songwriter, and the second for Johnson, 43, who has a 14-year-old daughter, Simone, with ex-wife and college sweetheart, Dany Garcia.
Garcia and Johnson split in 2007 after a 10 year marriage.
"We've been fortunate enough to spend the last 17 years together as a couple and look forward to spending the rest our lives together as best friends and business partners," he said at the time.
Johnson, who has remained friends with Garcia and whose trainer is her new husband, reportedly began dating Hashian that same year.
The former pro-wrestler turned actor has credited Hashian with helping him to achieve success.
"We do these stories and we talk so much about the business end, the success end, but then Lauren isn't mentioned and my daughter [Simone] isn't mentioned. I always like making sure we find the balance and my home life is in there and Lauren Hashian is in there and my daughter is in there. You gotta get the better half in there," the Scorpion King star told Esquire in 2014.
"With all the cool s--t and success that I've been lucky enough to get? That doesn't happen unless the home life is solid."
Johnson has yet to confirm the reports in public.