Is there an undo brush while doing a 3d sculpt in edit mode? I just want to undo a portion of my 3d sculpt.
The undos go in chronological order, so it’s not possible to cut out one action from the sequence and leave whatever you’ve done since. However, the next version of ZBrush (a free upgrade for all registered users), will include a smoothing brush that can be used to clean up a particular area of your mesh.
That doesn’t mean that you’re stuck without being unable to do things in the current version – just that it’s a little more difficult:
Mask the area that you wish to clean up
Invert the mask
Apply the Smooth deformation a time or six until it’s back to something you can work with
Clear the mask
Yep you bet, except it is called Ctrl+Z 
Their are two kinds of undo. One is for undoing changes made to 3D objects while in Edit mode (Tool Undo). And the other is for undoing changes to the canvas, like drawing and dropping objects (Doc Undo). You use Ctrl+Z for both types of Undo. Zbrush automaticaly selects which type depending on wether you are in Edit mode or not.
Go to Preferences Mem and set the number of undoes you would like stored. A higher number of undoes = more memory usage. While you are in Preferences Mem, make sure the Compact Memory slider is set close to the amount of free ram you have available when Zbrush starts (Check the Zbrush title bar at the top).
One of the cool things about undoes in Zbrush is that they are stored individualy for each 3D Object. That means you can edit one object, choose another to work on and then go back and undo changes to the first object. Just remember that undoes are not saved with the objects.
Welcome aboard 
Edit: Damn, too slow My stupid fat fingers again.
thanks guys for the quick reply!
The smoothing method will work for now.
In Maya, there’s an Erase brush in the Sculpt Polygon Tool where i can paint to revert to original mesh. Maybe one day Zbrush will have this feature 