Not that I know of, but I'm not using the latest version of Word. Have
you checked with Word VBA Help for your version?

For the two specific collections Bookmarks and Tasks, there's an Exists()
function (look it up in the VBA help). For all other collections, either you
iterate through the collection as Stefan said, or you can try to use the
style and catch the error if it doesn't exist, something like this:

Sub foo()
  On Error Resume Next
  Selection.Paragraphs(1).Style = _
     ActiveDocument.Styles("foobar")
  If Err.Number <> 0 Then
     If Err.Number = 5941 Then ' not exist
        ' let VBA handle any further errors
        On Error GoTo 0
        Selection.Paragraphs(1).Style = _
           ActiveDocument.Styles("Body Text")
     Else  ' other error
        MsgBox Err.Description
        Exit Sub
     End If
  End If

  ' let VBA handle any further errors
  On Error GoTo 0

  ' more code...
End Sub

Personally, I prefer the iteration method. It's quick enough that it won't
slow the macro noticeably. In contrast, error handling like the above can be
hard to get right.