With all cardio activities my HR does that at first. I tend to push myself to that limit and then increase the time just a little bit the next time. C25K may go too fast for you, but it's fine to repeat weeks. The body adapts quicker than you might imagine! My resting HR went from 85 down to 46 within about three months!

Where my HR used to shoot up to 185, now it "shoots up" to 130 and I'm working pretty hard at a mere 100.
This has been my favorite thing to watch about my weight loss efforts. I love to chart my HR and watch it come down over time. I get a bigger kick out of that than I do the scale.