The 19-year-old is looking for further first-team opportunities after making his Blues debut as a late substitute in a Europa League play-off second-leg tie against Portuguese side CD Nacional.
Holland-born Asante will link-up with the Cobblers when the January transfer window opens.
Birmingham manager Chris Hughton told the club's official website: "This is a good opportunity for Akwasi and will really benefit his development.
"He is one of a few young players we are currently looking at with regards to making decisions as to whether or not they go out on loan or not."
Cobblers boss Aidy Boothroyd told Town's official website: "Akwasi is a handful for defenders to play against.
"He is young, hungry and has a lot of pace. He has a good goalscoring record in reserve-team football and I think he can do a good job for us.
"I have seen him play for Birmingham reserves a few times and he has always impressed me. He is available for the game at Shrewsbury on Monday and he is raring to go."