It is not a requirement and from what i've read they really don't overlap. Sure there are some hardware overlaps like wiring types but no, you can go back and forth as long as you can remember that stuff.
As Wafflehammer said, new A+ is coming out in august which would mean the A+ exam you are studying for will be outdated soon, may be worth while just to hammer down on the Net+, pass it, then purchase a new A+ book and take that.