During October, 49.8 percent of the personal computers sold by retail stores in the United States contained an AMD processor, while 48.5 percent held a chip from Intel Corp., a report by Current Analysis Inc. shows. The San Diego, Calif., firm tracks sales at retail stores such as Best Buy.

Although it's not the first time AMD has surpassed Intel in one category or another at retail—AMD edged out Intel in desktops during September, for example, Current Analysis said—the October figures appear to show AMD riding a wave.

The Sunnyvale, Calif., company's retail market share surged from around 20 percent in June to almost 40 percent in July. Intel, meanwhile, saw its monthly numbers drop from near 80 percent in June to about 60 percent in July.

"Intel had no real low-end desktop offering in October. So it lost a lot of sales there," said Matt Sargent, the firm's director of research. Meanwhile, "The [Intel] Pentium 4 wasn't price competitive with [AMD's] Athlon 64. Those factors combined to submerge Intel in October."

NPD Group, which also measures retail sales, has spotted a similar trend for AMD and Intel. During September, the last month the firm has data for, AMD had 47.6 percent of desktops, while Intel had 46.9 percent, NPD figures show. But the situation reversed itself in notebooks, where Intel garnered 68.9 percent sales, while AMD had 21.7 percent.