In 3rd trimester and started noticing eye floaters while doing computer work - cause for concern?

Yes. In the third trimester the sudden appearance of visual changes is cause for concern. If floaters, there should be no major problem. However, some women mistake flashes of light or "stars" for floaters. Seeing bright or flashing lights is a sign of something more serious like high blood pressure. An OB provider should called and/or a woman should be seen immediately on labor & delivery for BP check.
Not Due to Pregnancy. Most likely not due to pregnancy...Although rarely pregnancy induced diabetes could cause some changes in the eye. Assume that the pregnancy is unrelated and make sure to get a dilated eye exam to ensure you have no retinal tear. You might even be able to figure out the cause.
Floaters. Most floaters are benign bits of vitreous gel moving about in the back of the eye. However, new floaters are cause for concern, since they may be associated with retinal tears. See your local ophthalmologist for a complete eye exam.