I have Bitdefender Total Security 2017 installed on my computer and today especially in the last 10 minutes I got over a hundred port scans (detected and blocked) which is weird cause I usually get like a ten during a whole day.
People are scanning the whole IPv4 Internet all the time, in the vast majority of the cases this can be considered "background noise" and can be safely ignored.
Security software tend to alert about events like this so that they can magnify their own importance by showing you how many "threats" (= harmless scans) they detected/blocked. These notifications should be even more suspicious if you are not connecting to the Internet directly but through a SOHO router for example, as these would filter actual port scans from your internal network so Bitdefender at your endpoint can't see them (there may be some techniques that'd allow intranet scans, but again, these are highly unlikely to come by).
This means that someone is trying to see what ports are open on your computer. There could be many reasons for someone doing this. For example, information gathering, vulnerability assessment to try and exploit vulnerable software, possible DoS attack vectors etc. Depending on your operating system you can enforce certain firewall rules to block certain scans or alternatively block the IP address launching the scans in question.