The Athletic reports that the Gunners are impressed with the Spanish defender who arrived in a loan deal from Flamingo.
Mari has impressed in the first few games he played before the COVID-19 league suspension.
The Gunners will activate the £10 million buy option in the deal to sign him permanently.
He would add to their depth at central defence for next season.
Arsenal will still likely go after a top rate centre-back in the market, with Dayot Upamecano their primary target.