If you want to zoom around the Prezi canvas with your keyboard you can use the shortcut keys.
Most shortcuts in Prezi are single stroke, which means there is no need to press any additional modifier keys (Alt, Ctrl, Command, etc.). Please note: shortcuts are turned off by default, click on the options tab in the top right corner of the Prezi Editor and click 'On' to enable them.
F - Draw frame, press again to change frame type (bracket, circle, rectangle or hidden)
L - Load a file on your canvas (image, pdf, video, swf)
S - Draw a shape, press again to change shape type (arrow, line, rectangle, circle, triangle)
P - Go to Path mode
1 - Zoom in
2 - Zoom out
3 - Rotate clockwise
4 - Rotate counter clockwise
Delete, Backspace - Delete selected object(s)
Left, Right, Up, Down - Move the selection 1 pixels
SHIFT + Left, Right, Up, Down - Move the selection 10 pixels
CTRL + S - Save prezi
CTRL + Z - Undo last action
CTRL + Y - Redo last undone action
CTRL + D - Duplicate selected object(s)
CTRL + C - Copy selected object(s)
CTRL + V - Paste copied object(s)
CTRL + SHIFT + M - Toggle screen ratio between the values: 4:3, 16:9, and off.
CTRL + SHIFT + C - Opens the Prezi CSS editor.
CTRL + SHIFT + D - Duplicates and flips your content, creating a mirrored version of your content (works for images and arrows but not text).
Esc (Escape key) - Finish current action or close open dialog