The highly-rated Norwegian has been missing for three months due to a leg injury and told arsenal.com: "It's really great to be back.
"I've been working extremely hard for three months now and the last two weeks I have trained both with the Reserves and with the first-team.
The 17-year-old confirmed that life remains good at the Club, and although match time has been limited, other areas of his development have gone from strength to strength.
"On a bigger picture, three months is not that bad of a time to be out," added Nordtveit. "I have been able to spend time in the gym and focus on other parts of my game.
"It hasn't made settling in more difficult at all actually. The physiotherapists have taken great care of me. Neil, Steve, the fitness coaches, everybody. They have all been really nice to me, taken care of me, always chatted to me, told me to think positive.
"Sometimes it has got me down, but I also have my family here all the time and that has kept me looking forward.
"Of course when you see the rest of the guys going out to train, and you know you're staying in doing a programme by yourself it's not so fun!"