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Apple (NASDAQ:AAPL) stock has seen a roaring comeback recently, with shares soaring about 28% in the past three months and hitting new all-time highs. At the time of this writing, shares are trading at about $139, well above their price of approximately $110 three months ago and significantly higher than the low $90s they hit last summer.

With the stock trading so much higher recently, is it still a buy? This is a good question, particularly following legendary investor Warren Buffett's recent move to load up on Apple, making it Berkshire Hathaway's (NYSE:BRK-B) (NYSE:BRK-A) second-largest equity holding.

Jet black iPhone 7 Plus

iPhone 7 Plus.Image source: Apple.

Reasons for optimism

Reinforced by Apple stock's 15% rise since its Jan. 31 first-quarter earnings release, investors seem pleased with the tech giant's performance recently. The recently ended quarter marked an important turning point for Apple as it returned to revenue growth, thanks primarily to a strong iPhone launch in September. The new iPhone 7 and 7 Plus models' popularity have helped the iPhone segment, which accounts for over 60% of total revenue, return to growth.

Chart showing year-over-year iPhone revenue growth by quarter

Data source: Apple quarterly SEC filings. Chart by author.

In its Dec. 31-ending holiday quarter, iPhone revenue and units increased 5% year over year as consumers bought up new iPhones. Apple sold 78.3 million iPhones, generating a record $54.4 billion in revenue for the segment, up from $51.6 billion in iPhone revenue in the year-ago quarter. The rise in revenue, combined with a $1.1 billion increase in its services revenue, helped Apple increase its total revenue 3% year over year.

The return to growth was a promising sign for Apple's ability to move product. But signs to be bullish didn't end there. Apple also guided for a 2% to 6% year-over-year increase in revenue during its second quarter, suggesting the return to growth may be here to stick around.

No longer the screaming buy it was

But Apple's stock price appreciation accompanying its solid business performance recently means the stock isn't the solid buy it was. Indeed, even Buffett seems to be rethinking how attractive Apple stock is after its sharp increase recently.

"I want to emphasize, we have not bought at this price. I mean, we quit buying when the earnings came out," Buffett said in a recent interview with CNBC. Importantly, Buffett was also careful to emphasize that Berkshire is "certainly not selling either."

Putting Apple stock's soaring valuation into perspective, the rising stock price has pushed its price-to-earnings ratio from about 11 one year ago to nearly 17 today.

AAPL PE Ratio (TTM) Chart

AAPL P/E Ratio (TTM) data by YCharts.

However, Apple's pricier valuation today shouldn't lead investors to immediately conclude the stock is no longer a buy. Apple stock still trades much more conservatively than many other companies. For instance, the average P/E ratio for stocks in the S&P 500 is 26. Combining Apple's conservative valuation with the company's recent growth, the stock is still a good long-term bet -- even at $139. But it's obviously not as good as a buy as it was around $100 a year ago or even at January's $120.