Depends on what is the computer speaker :)The worst case like a plastic case maybe 2 Watts distorting and not bass example would not do the Job. Except for checking later if your mix is working even on low grade speakers.The speakers (or headphones) you mix on should have a great resolution on detail level. You should be able to hear the tiniest EQ change or if the vocals are just a tad too loud or too much in the background. To achieve that the speaker should be as linear as possible. This usually leads to buying a near field monitor speaker. There are also so called computer speaker which are of high quality, but they tend to be costy. It simply makes more sense to buy a near field monitor as this would waste less money.Sadly this also includes your room and the placements of the speakers, as the bass response is heavily influenced by room acoustics and speaker placement. You will not be able to judge tiny changes in the midrange when the bass is so boomy due to misplacement or room modes it overlays everything. Or the other way round: you will not get the bass drum sound right if by placement there is a great dip (not eqable!) in the 80Hz region.Easy trick: Buy DSP controlled speakers which can also be linearized for your listening position. And place the speakers well. Like that you have the truest sound reproduction :) There is also a speaker linearization solution for present speakers: ARC from IK Multimedia. It works like Audissey in home cinema receivers (in fact it is Audissey put in software). It will linearize your speakers sound in your listening position or in a wider field in the room. As a feature it offers to simulate cheap/other speakers to check your mix later.