My iPhone6 screen touchs it self randomly

I have my Iphone 6 for at least a month, and for the last days, it I found that sometimes the screen "touches" its self randomly, and it it´s quite annoying. Open apps, write messeges, make calls, goes everywhere. I thought it was while plugged in, but not. I also tried to remove the case and it seemed to be ok that way. Should I use it without this case? Any other idea? txs.