As soosn as you select or deselect items in listbox, it will generate click event.

So try to declare a global boolean variable for detecting if the command button is pressed.

Like this;

VB Code:
  1. Dim bButtonClicked As Boolean
  2.  
  3. Private Sub Command1_Click()
  4.  
  5.     bButtonClicked = True
  6.     For i = 0 To lst_itm_cat.ListCount - 1
  7.         If lst_itm_cat.Selected(i) = True Then lst_itm_cat.Selected(i) = False
  8.     Next
  9.     bButtonClicked = False
  10.  
  11. End Sub
  12.  
  13. Private Sub Form_Load()
  14.  
  15.     bButtonClicked = False
  16.  
  17. End Sub
  18.  
  19. Private Sub lst_itm_cat_Click()
  20.  
  21.     If bButtonClicked Then Exit Sub
  22.  
  23.     'Your code for ListBox Click Event
  24.  
  25. End Sub