Is it normal for an Associate Editor to keep the paper for over a month after the reviews are done?
Unfortunately, turnaround for journals in most areas of computer science can be extremely slow. While I am not familiar with your area or this particular journal, the whole process can take anywhere from months to a couple of years. The typical reasons for the delay include:


Computer scientists care more about conferences than journals, so they focus their efforts on that, whereas journals have no hard deadlines;
Difficulty of finding reviewers (would-be reviewers say they don't have time); and
Reviewers who take months or years to submit their review (it sits on their backlog until the editor pesters them enough to complete it).


In your particular case, note that "awaiting AE decision" does require some work on the editor's part, or maybe even further discussion from the reviewers. So you can't assume that just because the status has changed, the paper is finished reviewing and ready to give back to you.

I would not worry about this. Consider putting your paper up on the arXiv. I have had journal papers take around a year for the whole process, and I have heard of some taking 2-3 years.