what would be the level of novelty of an undergraduate thesis? I would like to know what would be the level of novelty that one advisor should ask for an undergraduate student in Computer Science whom is aimed to make an Honours or Bachelor thesis?

For what I have discussed with some colleagues, it would be enough that from the chosen topic the student would feel comfortable for knowing the technique and the experimental methods that he would use. Instead to present something really original that would be in the field of a Master or PhD thesis.

What would be a set of guidelines regarding this issue?

Thanks
Requiring a new contribution to the field seems like an absurd bar to set for undergraduate students.  Not that it's impossible for an undergraduate to do so, but it shouldn't be the minimum standard you expect.

Of course it's possible that computer science is entirely different from my own field (economics), but I find it hard to believe it's that far off.  At the undergraduate level you're learning broad foundational material and techniques; at the master's level you're gaining a deep mastery of the material, possibly even focusing in a more specialized subset.  Then when completing a full PhD the student takes literally years to produce research that expands human knowledge within the field.

Requiring that a student meets PhD-like qualifications in their undergraduate work seems like it's setting them up for frustration, bad methods, or outright failure.  Maybe a truly exceptional student could do it anyway, with the limited time and resources available to them as an undergraduate, and more power to them obviously.  But that shouldn't be the requirement set for graduating.