He unsuccessfully appealed his conviction, sentence and a judge's decision not to grant him a discharge without conviction.
In April 2018 Mittal was granted a real estate agent's licence.
A conviction for a "crime of dishonesty" automatically rules a person out from holding a licence.
However, other convictions are considered on a case-by-case basis.
REA chief executive Kevin Lampen-Smith said the "particular circumstances" of Mittal's application were "fully researched, including review of the District Court sentencing decision and review of a relevant expert's risk assessment".
The REA then chose to issue the licence.
Associate Justice Minister Aupito William Sio said he would look into the matter.
"The actions of this individual are deplorable and unacceptable," he said.
"I am concerned about this issue.
"However, the details around the decision to license this agent are unclear at present.
"I intend to follow up with the Real Estate Authority for a full explanation."
The minister is currently overseas but would take the matter up when he returned.
Mittal did not respond to the Herald when contacted.
However, last week he repeated a claim made to the courts that the teenage victim instigated the offence.
He said coverage of his appeal had adversely affected his family.
Mittal, who described himself as an agent of "integrity, positivity, diligence and creativity", said he was due to be deported within a month.
The real estate company he was working for, Wallace and Stratton, said they had no idea about his conviction when he was employed.
Once they found out he was dismissed.
Managing director Ben Macky was also seeking an explanation from the REA as to how a child sex offender was granted a licence.
DO YOU NEED HELP?
If it's an emergency and you feel that you or someone else is at risk, call 111.
If you've ever experienced sexual assault or abuse and need to talk to someone contact the Safe to Talk confidential crisis helpline on:
• Text 4334 and they will respond
• Email support@safetotalk.nz
• Visit https://safetotalk.nz/contact-us/ for an online chat
Alternatively contact your local police station - click here for a list.
If you have been abused, remember it's not your fault.
