Creating a movie clip :
Create new flash document.

Draw a circle using the oval tool.

Select the circle using double click. Press F8 to convert to symbol.

Part 1 :

Click on the circle and Press F9. Actionscript Panel will open. Insert the following actionscript.

`onClipEvent(enterFrame){    diffx = _root._xmouse - this._x ;    diffy = _root._ymouse - this._y ;    _x += diffx ;    _y += diffy ;}`

_xmouse :   returns the x coordinate of the mouse.
_ymouse :
returns the y coordinate of the mouse.
_x            :
An integer that sets / stores the x coordinate of an object.
_y            :
An integer that sets / stores the y coordinate of an object.

variable diffx & diffy is used to store the distance between mouse's x & cordinate and object's x & y cordinate respectively.
_x += diffx ;
Assigns _x , the value of _x + diffx .
_y += diffy ;
Assigns _y , the value of _y + diffy .

Part 2 :

replace

`_x += diffx ;_y += diffy ;`

with

`_x += diffx / 5 ;_y += diffy / 5 ;`

Explanation of code :

_x += diffx / 5 ;
Assign _x , the value of _x + diffx / 5 ;( dividing the diffrence with a number decreases the speed of movment. Higher the number lower the speed. )
_y += diffy / 5 ;
Assign _y , the value of _y + diffy / 5 ;( dividing the diffrence with a number decreases the speed of movment. Higher the number lower the speed. )