Tovey is the record points scorer for the region with 951 in all competitions.
The 29-year-old made 117 appearances for the Dragons from 2007-12 and 2013-2016, with a year sabbatical to Cardiff Blues in between.
Tovey went on to join Scottish side Edinburgh before returning to Wales last summer to join Welsh Premiership club Keys where he played as a youth.
The former Wales Under-20 international is the sixth highest points scorer in PRO14 tournament history, two behind Felipe Contepomi, and is in contention for selection for the Dragons as they travel to Belfast to take on Ulster on Friday night.
“I’ve enjoyed being back in Wales with Cross Keys,” said Tovey. “But I’ve been training with the Dragons for a couple of weeks now and it’s good to step up to regional level.
“There have been plenty of changes here since I left, but there are still familiar faces and I’ve enjoyed slotting back in. I can’t wait to pull the Dragons shirt on again.”
Dragons head coach Bernard Jackman has seen injuries hit fly-half options Gavin Henson and Arwel Robson, leaving Josh Lewis as his only real No 10.
Tovey will now provide competition in that area.
“Jason has been in training with us this week and last week and he looks really sharp,” said Jackman.
“We’ve injuries to a number of our tens, so we’re lucky to have a player of his experience in and from our region who is available for us to call upon.
“We enjoy a good relationship with all the Premiership clubs in our region, regularly sending players out to them. On this occasion we’re grateful to Cross Keys for their support and allowing Jason to have this opportunity.
“He has great composure and game management from his experience. He knows when to find space and gives people inside and outside of him assurance. His talent with the boot is there for all to see, just look at his kicking record.
“The boys here who know him from his previous time at the Dragons were really enthusiastic about him coming back.”
Cross Keys head coach Morgan Stoddart said: “Jason has shown his class since his return to Wales and his kicking percentage is still up there with the best 10s in the PRO14, so it was no surprise when the Dragons got in touch.
“His experience has given us a boost, but the chance to work with the Dragons again is one we understand he can’t turn down.
“Whilst we have our own objectives as a club and squad in a competitive Premiership league, we’re fully supportive of what Bernard is trying to achieve at the Dragons both at senior level and within the region through the draft of player allocations.”
