As always with any question that asks you to examine the meaning of a particular text, it is important to look at the line in context so that you are aware of how it relates to the poem as a whole. Let us do this now:
O Attic shape! Fair attitude! with brede
Of marble men and maidens overwrought,
With forest branches and the trodden weed;
Thou, silent form, dost tease us out of thought
As doth eternity.
In Keats' mind, "thought" is what separates us from nature and "eternity," and helps us understand our own mortality and links us to the world of difficulty, hardship and toil. Contemplating such a symbol of pure beauty and aestheticism that has stood for so long and represents the eternal spirit of beauty can help to "tease us out" of this realisation as we contemplate the beauty before us. The line therefore speaks of the way in which laying our eyes upon such a symbol of eternal beauty helps us to transcend our human condition, albeit briefly, as we look upon an eternal example of beauty which stands in massive contrast to our own mortal existence.