Pop up notification of virus infected MacBook

I have been getting this pop up every time I open my MacBook. Is it a genuine or malware? Once I clicked the 'Start Scene' and it installed a software probably call Mac-keeper which scanned the computer and came up with frightening results and asked to buy the software to clean the computer. I uninstalled it but it keeps on popping up. What should I do? Thanks for your time and advice.