Armstrong was named as the SkyBet League One Player of the Month for August last week after scoring five goals, including two braces, in the first five games of the League One season.
"We're all delighted to learn that Adam has won and he definitely deserves it," Mowbray told reporters.
"He's had a fantastic month and we've all been really impressed with him since he joined the club in pre-season.
"Adam shows a fantastic humility on the training ground which means he is always listening to what you're saying and always looking to improve. With his natural enthusiasm for the game and his ability to learn, I'm sure we'll see more from him as the season goes on."
There had been speculation Armstrong would be called back to the Newcastle squad following the Magpies' dire start to the season in front of goal, however Newcastle manager Steve McLaren has opted not to exercise that option, meaning Armstrong will remain at Ricoh Arena until January.