"Academic bias" is another right-wing "When did you stop beating your wife" term. Using the term, even in defense, just repeats and ingrains the accusation.
Is there an academic tendency towards liberalism? Very likely, and for the same reason there is a tendency towards liberalism amongst mothers. Both are charged with a non-profit-making task, the development of children into responsible, educated, more independent adults. Both understand that they need to get the resources for this task from others without shackling the children into servitude in exchange. That means redistribution, bane of conservatives.
Some people have noticed that economics has the most conservative academics of all. Small wonder: economics departments have been the special recipients of conservative-funded welfare for long periods of time. The U. of Chicago and George Mason University famously have capitalist-funded economics departments, and the financial industry is a notorious funder of economics research. There is nothing comparable on the liberal side. There is a huge feeder system for conservative economics, with vast amounts of public propaganda promoting "free markets", chambers of commerce, innumerable think-tanks, and outreach programs to exceptional students that is unparalleled by moderates or liberals.