Try "I will be on the ground within five minutes". I'm assuming you're referring to when a flight is landing?

I'll be there in 5 minutes. "at ground" is wrong because you didn't use "the"....it should be "at the ground". However, as a Telugu speaker you don't use those words like "a" and "the" very easily. So why not just drop it. Say something else. Just say "there". "within" is wrong just because normally we say "in" five minutes, in an hour, in a year. We don't usually say "within five minutes". But it's not hard to understand you when you say it. So don't worry about it. The best thing to do in all cases is to say things as simply as possible.

If you're referring to the flight. " I'll be landing in about 5 minutes".