The forced question is "More secure" of what? Specifically if you mean "more secure of Microsoft related viruses and malware" the answer is "They won't affect Linux programs/services thus you won't need an anti-virus" and for a Desktop usage you can use an Anti-Virus such as the solutions mentioned in this question: What antivirus programs are available?.

Nevertheless it will be useful just for maintenance or fixing Microsoft related issues or infected files. Which will result more useful if you are sharing files with MS products users, such as Word, Excel, PowerPoint and more specifically: executable files.

If you plan to use Ubuntu as your main OS with no other scenery, you are safe from MS Viruses but we should yet pay attention to online exploits and other hacking techniques which may include the impersonation, personal data robbery and take much care of which places you trust for introducing credit card information.

I would recommend to use a web site analyzer such as the WOT Extension (Web of trust) for Google Chrome (may work also in Firefox, Opera and Chromium Browser) which will warn you if something's wrong in a website and block phising and other unsafe websites allowing you to know it from the results of a search in your favorite search engine as shown in the next screenshot in which we can see a small green donut beside the link's name which shows how trustable is the site:

WOT is a community based platform and now includes parental control when subscribed. BTW: I don't promote nor work for WOT. :) Just recommending.

Good luck!