The 25-year-old joined the Gunners from Bologna in the summer of 2021 and quickly established himself as the club's first-choice right-back under head coach Mikel Arteta following the departure of Hector Bellerin.
Tomiyasu has since had to deal with a number of niggling injuries and has subsequently lost his regular starting place to Ben White.
The Japan international has made a total of 73 appearances for Arsenal in all competitions, including 10 starts in 20 outings so far this season.
Tomiyasu, who scored his first goal for the club in a Premier League win over Sheffield United in October, is due to see his current contract at the Emirates Stadium expire in the summer of 2025.
However, journalist Fabrizio Romano reports that Arsenal are advancing into the 'final stages' of negotiations with Tomiyasu over a new long-term contract.
Romano adds that the Gunners intend to give Tomiyasu a pay rise and defender remains "100%" part of the clubs plans.
Tomiyasu has been linked with a possible return to Italy in recent weeks, with AC Milan believed to be one club interested in his services.
However, Arsenal are said have no interest in letting Tomiyasu leave the club in January and hope to tie him down to a new deal soon.
In November, Arteta expressed his desire to keep hold of Tomiyasu as he believes the defender is an invaluable member of his first-team squad.
"I really want him to stay. I value the player a lot, I really like him. I think he's loved and respected by everybody at the club," Arteta told reporters.
"He's getting a lot of minutes now, he's getting his availability to the level that we need for him to make an impact in the team and I think he will continue to be with us."
Arsenal will have to cope without Tomiyasu for the next month or so, though, as the defender has been called up to the Japan squad for the Asian Cup.