When Karen Mills announced in February that she would not stay on for a second term as head of the U.S. Small Business Administration, she still planned to remain in her post until the government agency named a replacement.

But those plans apparently changed as Mills told the SBA staff on a conference call Wednesday that she will be leaving her post at the end of August.

Mills will continue work on economic issues surrounding entrepreneurship at both Harvard Business School and Harvard’s Kennedy School starting this fall, according to a statement from Emily Cain, press secretary for the SBA. In addition, Mills will “pursue business opportunities,” Cain says. Specifics were not provided.

Related: Karen Mills to Leave the SBA

The White House says only that it has no personnel announcements to make, according to Bobby Whithorne, a White House spokesperson. But the SBA says it is working to find a replacement. “The agency is working closely with the White House on transition plans and on the appointment of a successor,” Cain says.

Many in the small-business community have expressed frustration with the White House for prolonging the new chief's appointment.

"There is no excuse for the administration's inaction. Sadly, it appears the stated support for Main Street by the President during election was only pandering,” says Bob Coleman, the editor of the small-business-lending industry newsletter The Coleman Report. “It is ridiculous that the White House can't find a qualified nominee after five months. There are a number of worthy candidates available from both the public and private sector.”

Rep. Sam Graves (R, Mo.), the chairman of the House Small Business Committee, called it “very disappointing” that the Obama administration had not come up with a new leader for the SBA yet. “The SBA performs an important role for many small businesses, and the administration should make small businesses a higher priority by finding a new administrator as quickly as possible,” Graves says in a statement.

Related: Karen Mills on the SBA: Successor Needs to Get the Word Out

Administrator Mills, a long-time Maine resident, has been largely credited with revamping the SBA. Four years ago when Mills arrived in Washington, D.C., the SBA was a very different agency. The U.S. economy was weak and getting weaker. Pipelines of credit were virtually frozen for all businesses, and small businesses especially struggled to get the financing they needed. Mills’s first priority was to help the nation’s small businesses get access to capital, and she spearheaded several stimulus programs to jump-start lending.

In 2011, the SBA guaranteed more than $30 billion in loans to more than 60,000 small businesses, setting a record for the agency.

While the economy has not yet returned to pre-recession strength, it is showing signs of improvement. Mills’s primary task upon taking office was to implement an emergency plan to get capital to Main Street. The incoming chief’s primary goal for the next four years, according to Mills, should be spreading the word about what the SBA has to offer. She says that not enough small businesses understand how the federal agency can help them.

Before she was sworn in as head of the SBA in 2009, Mills was president of the private-equity firm MMP Group, which invested in businesses in the consumer products, food, textiles and industrial components industries.

Mills has a personal interest in the benefits of economic “clustering,” where businesses and research organizations band together to mentor each other and work together. In 2010, Mills launched a pilot program for investing in groups of businesses throughout the U.S. A recently released third-party analysis of the two-year program found that businesses involved in the clusters generated jobs and revenue faster than similar businesses working in isolation.

Related: This Kind of Cluster Could Actually Help Your Business