Is the iPad now cannibalizing the Mac?

An analyst sees the first sign of trouble in July's retail sales data

Amid the good news for Apple (AAPL) in the NPD Group's report on domestic retail sales for the month of July, Morgan Stanley's Katy Huberty spots what she thinks may be a small dark cloud.

In a report to clients issued Monday, Huberty notes that sales trends for the broader PC market -- which includes Apple and everybody else -- were mixed. Consumer PC sales decelerated to 3% year over year from 6% in June and 8% in May -- not a good sign as we head into the prime back-to-school buying season. Sales to business, however, rose 39% year over year, allowing overall PC sales growth to hold steady at 11%.

The good news for Apple is that Mac sales were up 14% year over year in July -- better than both June (11%) and the overall PC market (also 11%).

However, July's 14% growth is down from the Mac's previous three-month average of roughly 25%. Huberty's analysis:

"iPad momentum is likely contributing to the moderation of both broader PC and Mac unit growth."

Huberty had previously found evidence that the iPad was cutting into sales of iPod touches, netbooks and even Microsoft (MSFT) Windows PCs. This is the first time we've seen anyone suggest that they might also be cannibalizing Mac sales.

See also:

• Hello iPad, goodbye netbook
• How the iPad gobbles up netbook sales

[Follow Philip Elmer-DeWitt on Twitter @philiped]