VBAで、ある列に入力されている数値の平均値を求めるコードを教えてください。

こういう事でしょうか？

Public Sub sample()

    Dim i
    i = Sheet3.Cells(1, Columns.Count).End(xlToLeft).Column
    If Sheet3.Cells(1, i).Value <> "" Then i = i + 1 'A1が空白ならiを1とする

    Sheet2.Range("A1").CurrentRegion.Copy 'Sheet2のデータをコピー
    'Sheet3に貼りつけ
    Sheet3.Cells(1, i).PasteSpecial Paste:=xlPasteValues, _
    Operation:=xlNone, SkipBlanks:=False, Transpose:=False
    Sheet2.Cells.Clear '記録用シートの初期化

    Call getAverage(i)

End Sub

Private Sub getAverage(ByVal lBeginCol As Long)

    Const TARGET_SHEET_NAME As String = "Sheet3"

    Const COL_OFFSET        As Long = 2

    Dim sHeader     As String
    Dim lCol        As Long
    Dim lEndRow     As Long
    Dim lTargetCol  As Long

    lCol = lBeginCol

    With ThisWorkbook.Worksheets(TARGET_SHEET_NAME)
        sHeader = .Cells(1, lCol).Value

        Do Until sHeader = ""
            lEndRow = .Cells(1, lCol).End(xlDown).Row

            lTargetCol = lCol + 1

            .Cells(1, lTargetCol).Value = WorksheetFunction.Average(.Range(.Cells(2, lTargetCol), .Cells(lEndRow, lTargetCol)))

            lCol = lCol + COL_OFFSET

            sHeader = .Cells(1, lCol).Value
        Loop
    End With

End Sub