Mkhitaryan has made 19 appearances in all competitions since joining from Arsenal in September and has recently returned from injury.
Roma will have the Armenia international available for the closing weeks of a campaign that was delayed for several months due to the coronavirus pandemic, while there is also a preliminary agreement for 2020-2021 in place.
"I'm very pleased," Mkhitaryan - who has started the previous two games - said.
"I'm happy to extend my stay here, because I still have things that I haven’t achieved yet that I want to achieve.
"I'm looking forward to it."
Mkhitaryan moved to the Gunners from Manchester United in January 2018 as part of the deal that sent Alexis Sanchez in the opposite direction.
Roma sit fifth in the Serie A table but are nine points adrift of fourth-placed Atalanta. Paulo Fonseca's squad are still in the Europa League too, with a one-off tie against Sevilla to come early next month.
"We are happy that Henrikh has decided to stay with us, and help us continue to grow," Roma CEO Guido Fienga said.
"The club's targets have not changed and we always want to have players at our club, like Micki, who show their desire, professionalism and determination, who represent our club and our fans in the right way."